Move serverless metrics from "serverless" page into "metrics" page

Problem to solve

Currently, metrics generated by GitLab serverless show up under "operations>>serverless". All other metrics show up under "operations>>metrics". This may be confusing for users.

Intended users

developers, operators

Further details

Proposal

Move serverless metrics from the "serverless" page into the "metrics" page. As it's possible that a serverless application may be comprised of many serverless functions, we can show a full list of deployed functions and have the user drill down.

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references