[C/OM] Update docs to reflect the deprecation of the New Relic monitoring integration

Description

Description

Effective June 16th, our monitoring integration with New Relic will no longer work. We would like to provide advanced warning to our users, so they can transition off of this intergraion before that date. 

To help users make the transition, we would like the docs pages to reflect that the New Relic integration will be deprecated, point to this NR announcement explaining the reasons for this deprecation, and link to this NR integration with MongoDB as an alternative. Note that the New Relic integration applies to CM, OM, and Atlas. 

We plan to send an email notifying users of this deprecation this Tuesday, 4/13. Ideally, the docs changes would coincide with this notification. We also need the changes to be reflected in the docs so we can link to them in the UI, where we will also alert users of the deprecation. 

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)