Sync mailinglists using Google Admin SDK

One-sentence description

Motivation

Because we switch to GSuite

Desired functionality

Sync the mailinglists to

Suggested implementation

We currently have a syncmailinglists scripts in the serverconfig repo that uses the mailinglists API. Instead of syncing to Mailman we want it to sync to GSuite. And by replacing the script with a management command we can move this code to concrexit.

You probably want to make sure this has 100% test coverage.

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