Propagate trace context to Jenkins build agents

[cyrille-leclerc]

Propagate trace context to Jenkins build agents so plugins that execute code in the build agent have end to end view on their code execution.

It's disabled by default, to enable it, set the following configuration options through the Jenkins OTel Plugin Config screen:

otel.instrumentation.jenkins.remoting.enabled=true
otel.instrumentation.jenkins.agent.enabled=true

Testing done

Submitter checklist

• [x] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did
• [ ] Link to relevant issues in GitHub or Jira
• [ ] Link to relevant pull requests, esp. upstream and downstream changes
• [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[cyrille-leclerc]

@timja FYI I just need to add documentation on the feature flags otel.instrumentation.jenkins.agent.enabled=true|false and otel.instrumentation.jenkins.remoting.enabled=true|false and it will be ready for review.

[cyrille-leclerc]

@kuisathaverat please review