installing discourse to take over from mailman and import archive, users and lists from mailman

The current instance of mailman is past its sell-by-date for jalview mailing lists.
We want to migrate to our own instance of Discourse hosted locally.
Migration should carry across as much as possible in as sensible a mapping as possible, e.g. users, archive, threads.

This tool should make this achievable: https://lab.enough.community/discourse/mailman2discourse

Discourse: https://www.discourse.org/
https://github.com/discourse/discourse_docker