Set all CODEOWNERS sections to optional
Following a conversation with @phikai and @kwiebers somewhat related to https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/1039
We discovered recently when enabling the CODEOWNERS approval in the www-gitlab project that all open merge requests use the CODEOWNERS file from the source branch.
Currently the CODEOWNERS approval is switched off/globally set to optional for the gitlab project, but by setting each section of the CODEOWNERS File itself to optional, it will make the transition considerably easier if/when we decide to enable/switch it on.