Revert "Revert "Update code quality documentation""

What does this MR do?

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• N/A Changelog entry added, if necessary
• Documentation created/updated
• N/A Tests added for this feature/bug
• N/A Conforms to the code review guidelines
• N/A Conforms to the merge request performance guidelines
• N/A Conforms to the style guides
• N/A Conforms to the database guides
• N/A EE specific content should be in the top level /ee folder
• N/A For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?