Add gitlab/CODEOWNERS for requiring maintainer approvals

This file will allow configuring the protected branches to require package maintainers to approve changes to their packages.

The list was obtained by grepping the APKBUILD of each package. I only included 'device/community' and 'device/main'. This could be expanded to include other packages in pmaports.

I think something like this is necessary, for insuring that package maintainers are properly notified and provide approval for MRs that make changes to things that they are ultimately responsible for.