Use `jenkins.baseline` to reduce bom update mistakes

[strangelookingnerd]

Use jenkins.baseline in pom.xml

This change is proposed by the plugin archetype and makes maintenance of jenkins.version and bom a little easier.

Testing done

None. Rely on ci.jenkins.io to test it.

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
• [x] Link to relevant issues in GitHub or Jira
• [x] Link to relevant pull requests, esp. upstream and downstream changes
• [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[strangelookingnerd]

@jenkinsci/postbuildscript-plugin-developers Kindly requesting a review.