Check for groups.io presence

(Most) CNCF projects are expected to have a presence on cncf.groups.io. I propose a check to ensure there's at least one mailing list created that follows the pattern of `cncf-{project-name}-*` (ex. `cncf-buildpacks` or `cncf-buildpacks-dev` would both be valid)

There are some exceptions that we need to think about however (mainly, older/graduated projects). Kubernetes uses Google Groups, for example. So perhaps this check should be (initially) only valid on projects that have been adopted starting in 2020 and newer?

No file, test, or entry point is named. Start by locating the existing project health checks and how project adoption dates and exceptions are represented; resolve the cncf.groups.io naming rule and older-project exclusions before implementation. Done means the check consistently handles valid mailing lists and documented exceptions.

Written by the indexing model from the issue text.