[JENKINS-74098] Remove inline JS script and legacy onClick handler

[shlomomdahan]

Jira: JENKINS-74098

What has been done

1. Remove the inline JS <script> tag as well as its corresponding legacy onChange handler to improve CSP compatibility.

Screenshots

Before
After

How to test

1. Create a freestyle project
2. In Post build actions select Plot build data
3. In the Plot Group enter a name (ex. "test") and use that same plot group name to create 2 or more plots.
4. Save the configuration, go to the project page and select Plots from the left hand navigation menu
5. in the "jump to" selector, select a plot and observe the page jump to the location of that plot

Checklist

• Git commits follow best practices
• Build passes in Jenkins
• Appropriate tests or explanation to why this change has no tests
• Pull Request is marked with appropriate label (see .github/release-drafter.yml)
• JIRA issue is well described (problem explanation, steps to reproduce, screenshots)
• For dependency updates: links to external changelogs and, if possible, full diffs

[MarkEWaite]

Thanks!