Update troubleshooting guide for resource groups

What does this MR do and why?

This introduces additional troubleshooting guides around the issues reported in Job stuck waiting for resource (#425819 - closed).

Screenshots or screen recordings

How to set up and validate locally

Documentation setup and testing: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md

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.

Related to #425819 (closed)