[JENKINS-53890] Add lockable resources support on metrics plugin

It would be great to emit metrics for lockable resources:

• jobs/tasks waiting for lock on a resource
  
  and/or:


• resources availability/usage


• labels availability/usage

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Originally reported by thomas_deepomatic, imported from: Add lockable resources support on metrics plugin

• status: Open
  
• priority: Minor
  
• component(s): lockable-resources-plugin, metrics-plugin
  
• resolution: Unresolved
  
• votes: 0
  
• watchers: 1
  
• imported: 20251217-081411
  

It would be great to emit metrics for lockable resources:



	
jobs/tasks waiting for lock on a resource

and/or:

	
resources availability/usage

	
labels availability/usage

Start by reviewing the lockable-resources-plugin and metrics-plugin integration points to determine how metrics are currently exposed. Define which waiting-job, resource, and label availability or usage metrics are in scope, then add coverage showing the selected metrics are emitted.

Written by the indexing model from the issue text.