Draft: Explain relation of approval rules and codeowners

What does this MR do?

A user said that if Codeowners approval is made optional but if “you set eligible approvers to a non-zero amount” the approval becomes mandatory. I am not 100% sure how he means that. I speculate it is about this setting: https://docs.gitlab.com/ee/user/project/merge_requests/approvals/rules.html#code-owners-as-eligible-approvers.

• I think the user may have used approval rules where he shouldn’t have used them. Unlike CODEOWNER approvals, approval rules apply to entire branches and cannot be refined to apply to specific parts of your code base.
• I can see how this combination of optional approval in the codeowner file combined with requiring approval by eligible approvers can create confusing results.
• I think it might be good to bring codeowner documentation and approval rule documents closer together. UP FOR DISCUSSION. Please, chime in @phikai and @aqualls.
• But at least on the approval rule side provide a similar intro sentence as on the codeowner documentation side (see paragraph below video) that explains the purpose of each and how they work together. (THIS IS WHAT THIS MR IS ABOUT)

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