[JENKINS-73879] Remove inline JavaScript for rootPOM validation

[yaroslavafenkin]

JENKINS-73879

Testing done

I thought recording a video for such change would be an overkill, so I'll provide some screenshots. Let me know if it's enough.

Before the change

Each time I trigger a validation on the rootPOM field on the configuration page of a Maven Project an error in the console appears:

Checking the Content Security Policy report (provided by Content Security Policy) we can see there's a violation:

Parameter received on the server side:

After the change

Triggering validation multiple times on the project configuration page yields no errors in the console:

Content Security Policy report remains clear:

Value of the parameter is still received correctly by the server:

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!