Fix owners for scoped maintainers

What does this MR do?

Switches the scoped maintainers as owners from optional to required. The optional setting was a mistake on my part. We want them to actually be able to approve and merge the scoped changes, which optional does not do. Optional in our setup just ends up being a recommendation. We want to give them the power to approve and merge their scope.

Related issues

Part of gitlab-org/distribution/team-tasks#1253 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, follow the instructions in the "Reviewer Roulette" section of the Danger Bot MR comment, as per the Distribution experimental MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.