Track epic labels change action on usage ping

What does this MR do?

It adds tracking for changing labels on epics.

Does this MR meet the acceptance criteria?

Conformity

• 📋 [Does this MR need a changelog?](https://docs.gitlab.com/ee/development/changelog.html#what-warrants-a-changelog-entry
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related to #292253 (closed)