Deprecate RuleBasedRoutingSampler in favor of ComposableRuleBasedSampler

Deprecate RuleBasedRoutingSampler in favor of ComposableRuleBasedSampler, which implements the same concept now standardized (although still in development) in the spec.

ComposableRuleBasedSampler is still incubating in the spec and in opentelemetry-java. I don't think we should have a delete time table for RuleBasedRoutingSampler until ComposableRuleBasedSampler is stable. Still, I think we should deprecate to:

• Stop adding new features to RuleBasedRoutingSampler, instead encouraging development on ComposableRuleBasedSampler and incentivizing stabilization.
• Start a long deprecation window so users have plenty of time to migrate.

Using the declarative config example snippet from the RuleBasedRoutingSampler readme, here's the before / after switching to ComposableRuleBasedSampler:

RuleBasedRoutingSampler:

tracer_provider:
  sampler:
    parent_based:
      # Configure the parent_based sampler's root sampler to be rule_based_routing sampler.
      root:
        rule_based_routing:
          # Fallback to the always_on sampler if the criteria is not met.
          fallback_sampler:
            always_on:
          # Only apply to SERVER spans.
          span_kind: SERVER
          rules:
            # Drop spans where url.path matches the regex /actuator.* (i.e. spring boot actuator endpoints).
            - action: DROP
              attribute: url.path
              pattern: /actuator.*

ComposableRuleBasedSampler:

tracer_provider:                                                                                                                                                                                                                                                                                                                                                                                                                                          
 sampler:                                                                                                                                                                                                                                                                                                                                                                                                                                                
   parent_based:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
     root:                                                                                                                                                                                                                                                                                                                                                                                                                                               
       composite/development:                                                                                                                                                                                                                                                                                                                                                                                                                            
         rule_based:                                                                                                                                                                                                                                                                                                                                                                                                                                     
           rules:                                                                                                                                                                                                                                                                                                                                                                                                                                        
             # Drop SERVER spans whose url.path matches /actuator* (spring boot actuator endpoints).                                                                                                                                                                                                                                                                                                                                                     
             - span_kinds:                                                                                                                                                                                                                                                                                                                                                                                                                               
                 - server                                                                                                                                                                                                                                                                                                                                                                                                                                
               attribute_patterns:                                                                                                                                                                                                                                                                                                                                                                                                                       
                 key: url.path                                                                                                                                                                                                                                                                                                                                                                                                                           
                 included:                                                                                                                                                                                                                                                                                                                                                                                                                               
                   - /actuator*                                                                                                                                                                                                                                                                                                                                                                                                                          
               sampler:                                                                                                                                                                                                                                                                                                                                                                                                                                  
                 always_off:                                                                                                                                                                                                                                                                                                                                                                                                                             
             # Catch-all: fallback to always_on                                                                                                                                                                                                                                                                                                                                                     
             - sampler:                                                                                                                                                                                                                                                                                                                                                                                                                                  
                 always_on: 

Start with samplers/src/main/java/io/opentelemetry/contrib/sampler/RuleBasedRoutingSampler.java and its README configuration example, then compare the linked ComposableRuleBasedSampler API. Check the sampler module's existing deprecation and API tests before documenting the migration path. Done means the older sampler is deprecated with a clear reference to the composable replacement and relevant checks pass.