Maintainer mailing lists - work

We need the following features added to manage the mailing list estate for CNCF Project maintainers.

This iteration will focus on the maintainer mailing lists.

The set of lists named `cncf-_{PROJECT-NAME}_-maintainers@lists.cncf.io` are a key comms channel for the CNCF to message CNCF projects to inform projects of upcoming events, deadlines for submissions to particpate in events, talks and grant applications.

Where _{PROJECT-NAME}_ is the slug name of a CNCF Project.

## groups.io challenges

### no site-wide administrative access to all CNCF lists

In groups.io, the service that we use for mailing lists, CNCF Projects Team Staff (and select LF Staff) require access to manage lists; each Staff member MUST be subscribed to the list and MUST have Owner access to act as administrators of the lists.

Additionally, there is no way of templating a "team" of adminsistrators in groups.io
Finally, there are no settings templates to descirbe a type of mailing list.

The maintainer-d groups.io plugin can handle this as follows:

1. Define mailing list staff team that can be granted role-based access to maintainer mailnig lists
2. Create settings templates to describe how the CNCF setsup a project maintainer mailing list
3. Create a gitops-based workflow that will allow CNCF Staff to submit messages as Pull Requests to a repo so that messages can be reviewed before the are sent to the lists on groups.io

## Workflow challenges
### Message content review
We need a way of reviewing message content to ensure that all links work, deadlines have not passed etc.

At present message content review is done adhoc by the person who releases the messages from the Pending Message Queues on groups.io a gitops-based workflow would help with this give all CNCF Staff access.

### Post mail-shot reporting is ad-hoc at present

We have commandline tooling in [cncf/groups-admin](https://github.com/cncf/groups-admin/) and we can leverage that here for this work but it would be better to create a report of what mailing lists received the message on groups.io.

## Initial tasks
[ ] Add staff members to maintainer-d
[ ] lift the groups.io client from groups-admin
[ ] create an settings template for maintainer mailing list (we are focusing here on the main maintainer mailing lists for now but from the project perspective, some projects have security mailing lists and the CNCF manages other mailing lists also. Theses are mailing lists are out of scope for this work)