[JENKINS-73956] Extract inline event handlers from LegacyJobConfigMigrationMonitor/manage.jelly

[yaroslavafenkin]

https://issues.jenkins.io/browse/JENKINS-73956

Testing done

To activate the monitor I've installed the version of the plugin that does not have the fix for SECURITY-988, i.e. 1.43.1.
I've set up src job that does echo 123 > file.txt and archives the artifacts. Other jobs have Copy artifacts from another project step with src being the project name to copy artifacts from.
In security configuration I've enabled project based matrix auth strategy (from matrix-auth). I've added a user that has Item.READ and Item.BUILD permissions. For the src project that archives the artifact I've taken that permission away by enabling project-based security and setting "Do not inherit...". I've built all the jobs at least once, starting from the src.
After that I've upgraded the plugin to the latest version. Logged in as the user I've set up earlier and built the projects I had access to (all but src). That triggers the monitor. Logged back in as admin and navigated to /administrativeMonitor/copyArtifactLegacyJobConfigMigration/manage.

Before & after

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• 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

[basil]

Thanks for the PR!