Harmonize GitHub teams and roles

[timuthy]

What would you like to be added:
After switching to an declarative approach for maintaining the Gardener org membership and teams, a harmonization of teams and roles across Gardener repos ought to follow:

• Each repository should (at least) come with two dedicated teams, projecting the admin and maintainer role (also see Repository roles for an organization)
  • <repo-name>-admins
  • <repo-name>-maintainers
• Parent teams are possible, e.g. gardener-networking-maintainers = {gardener-extension-networking-calico, gardener-extension-networking-cilium, ...}
• Each team should only consist of members as their membership is maintained by Peribolos, making maintainers obsolete
• The structure and teams must be compatible with Automate maintenance of OWNERS_ALIASES files #5.

Why is this needed:
Understandable, documented and standardized teams and roles across repos makes membership requests and maintenance significantly easier.

[timuthy]

/cc @oliver-goetz

[oliver-goetz]

We could also consider a team which provides write access since this is required to edit issue and PR descriptions of others (e.g. to work on umbrella issues).

[dimityrmirchev]

Each repository should (at least) come with two dedicated teams, projecting the admin and maintainer role

Do we really need an admin role for each repository? If we have sufficient automation for repo setup the admin role should not be of much use for regular activities. Or is there a function that needs to be performed by an admin on a (semi)regular basis? Maybe security advisories if those cannot be handled by another role? My proposal would be to directly map two roles (can be per repo or per area) via a convention, e.g.

• gardener-maintainers (approvers) -> gives you GH write (or maintain if really needed) access and also writes you as an approver in the OWNERS file
• gardener-reviewers -> gives you GH read (or no access) access and also writes you as a reviewer in the OWNERS file

And ad-hoc teams such as:

• gardener-triage -> grants GH write access, not related to the OWNERS file, can be given to people that need to redact issues or release notes, etc
• gardener-release-responsibles -> grants GH write access, not related to the OWNERS file, can be given to people that need to to fulfil the release responsible duties, but are not part of the gardener-maintainers (approvers)