Support additional telemetry metadata variation types

We have some tests with some variability that can't currently be well handled by the existing metadata system - for example runtime metrics. In runtime-metrics we are currently trying to separate the telemetry by runtime variation but using the same mechanism (metadataConfig) as we do for configuration-based variations.

On top of this, we aren't running exhaustive tests for the runtime variations, and are sometimes seeing some churn in the emitted attributes.

See:

• https://github.com/open-telemetry/opentelemetry-java-instrumentation/pull/19150#discussion_r3549582478
• https://github.com/open-telemetry/opentelemetry-java-instrumentation/pull/19236/changes#diff-d4a9a82e2e49dddcd092fd546bd57ce2537c32079541611c164a0848fe61e2c1L16084

We should determine if we need some additional when capabilities that can support things like runtime variations on top of standard config variations.