[JENKINS-42798] Add support for cleaning workspace when it is locked.

[johnou]

This MR introduces a new per-job configuration option: "Cleanup workspace when locked". When enabled, the plugin checks for workspace locks in the subversion working copy - typically caused by interrupted operations like svn update or commit. If a lock is found, the plugin runs svn cleanup before proceeding.

Testing done

Tested by copying one of our large jobs workspaces into a duplicate job, starting a build, interrupting it during an update, and finally running it a second time -> locks are broken as expected (took 9 minutes but in our case the incremental job takes several hours when the workspace is wiped).

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

[johnou]

@basil ptal when you get a moment.

[basil]

Hi @johnou, unfortunately we don't have any developers actively reviewing incoming pull requests for this plugin. We don't want your pull request to be in limbo forever; you can step forward to become a maintainer of this plugin following the instructions here:

https://www.jenkins.io/doc/developer/plugin-governance/adopt-a-plugin/

[gounthar]

@johnou

Please let us know if we can assist you with the process of becoming a maintainer.