In-product shows Monitor features that are being deprecated

Summary

This issue keep tracks of in-app notification and change requirements for Monitor related deprecations in %15.0.

Proposed Changes

1. Display an alert at the top of the Metrics, Logs, Tracing, and Settings > Monitor pages.
2. Alert will communicate what's happening, how this will impact people, and what the plan is for replacing these features:

• scheduled for removal, links to - &7188 (closed)
• learn more about Opstrace, links to - &6976 (closed)