CDRIVER-5529 update release instructions to account for new rulesets

[eramongodb]

Resolves CDRIVER-5529. Followup to mongodb/mongo-cxx-driver#1385.

The rulesets for the C Driver repository are nearly identical to those implemented for the C++ Driver, re-summarized here:

• Joining the @mongodb/dbx-c-cxx-releases team during a release allows one to bypass to the following rulesets:
  • "Restrict Creations" (branches and tags) to create new release branches and tags.
  • "Require a Pull Request" (new and active branches) to directly push to (new) release branches.
• "Restrict Deletions" apply to all branches and tags without exception.
• "Restrict Updates" applies to all tags without exception and to an inclusive target list of stale branches which may be "locked" from any further changes.
• "Require a Pull Request" applies to all branches, except as bypassed described above, and excluding the debian/unstable and gh-pages branches (always direct-pushable).

Note

"Require a Pull Request" also applies the following rules:

• "Require linear history"
• "Required approvals" (set to 1)
• "Require review from Code Owners"
• "Allowed merge methods" (Squash or Rebase)

No changes to how release tags are created appear to be strictly necessary atm given the release scripts already GPG-sign the release tag using the current git author's signing key. This is unlike the C++ Driver's currently-proposed solution which uses the Release Signing Key instead. We may want to consider switching to using the Release Signing Key for the C Driver as well in the near future to improve the usage experience for users who wish to validate the signature against a well-known, dedicated public key (provided by https://pgp.mongodb.com/) rather than individual developers' public keys. Filed CDRIVER-5994 to track this followup work (which must be individually and manually uploaded to one or more public keyservers for visibility...? GitHub snippets? public wiki page? ¯\_(ツ)_/¯).

[kevinAlbs]

LGTM. This reminded me to remove myself from the dbx-c-cxx-releases team.