Add helpful text to project select modal

What does this MR do and why?

It was unclear the impact of adding projects to the environments project, so some text has been added to make it clear to users that adding here also adds to the operations dashboard and vice versa.

Changelog: added

Screenshots or screen recordings

How to set up and validate locally

1. Navigate to environments dashboard
2. Add a new project

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.

#12869 (closed)