Use 'Changes' page from core

[janfaracik]

jenkinsci/jenkins#11277 released as part of 2.537 unifies the 'Changes' page across core and this plugin, so we can do away with the duplicated code in here.

👋 jenkinsci/bom#6285 is delayed at the moment, so unsure on the best approach here: point at bom-weekly or just hold out until bom-2.541.x released. This PR isn't urgent but it would be nice for users upgrading to 2.541.1 and using the experimental UI.

Testing done

Now that we're using core's Changes page, we benefit from the work done to add support for the experimental Run UI.

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 demonstrate the feature works or the issue is fixed

[janfaracik]

Will reopen once changes have been made to core. Moving changes.jelly to Run/