Add self-monitoring notice in metrics form

What does this MR do and why?

As per #353145 (closed), the deprecation notice will need to be added to the form in metrics page.

Screenshots or screen recordings

How to set up and validate locally

1. Go to On the Admin > Settings > Metrics and profiling page (where self-monitoring is enabled)
2. Expand Self-monitoring and see the alert.

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.

Related to #353145 (closed)