Add reply button to abuse report notes

What does this MR do and why?

• Resolves sub-task 5 of https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/168 and follows-up from !135533 (merged)
• Adds a reply button to notes on an abuse report.

Screenshots or screen recordings

replying

How to set up and validate locally

1. In the rails console, enable the feature flag abuse_report_notes

> Feature.enable(:abuse_report_notes)

2. Log-in as root and navigate to /admin/abuse_reports and click on any abuse report. If there aren't any abuse reports available, you can create one:

AbuseReport.create(user_id: User.last.id, reporter_id: User.first.id, message: "obvious spam")

3. Try to add a new comment and then refresh the page.
4. Then try to reply to that comment.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.