docs: Reduce duplication between MR guidelines and Definition of Done

What does this MR do and why?

It bothered me that we had so much duplication between MR guidelines and Definition of Done in our documentation.

This MR tries to reduce this by not removing any useful information.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.