In-product shows Self-Monitoring is deprecated

Summary

This issue keep tracks of in-app notification for support removal of self-monitoring.

Proposed Changes

1. Display an alert in the following two locations:
   1. On the Admin > Settings > Metrics and profiling page (where self-monitoring is enabled)
   2. When self-monitoring is enabled, and the Monitoring project has been created, display the warning on the project information page.
2. Alert will communicate what's happening, how this will impact people, and what the plan is for replacing these features:

• deprecation link, links to - https://docs.gitlab.com/ee/update/deprecations#gitlab-self-monitoring
• removal link, links to - #348909 (closed)
• Opstrace, links to - &6976 (closed)