Automate BBB settings

Big Blue Button is not as tightly integrated as it would be desired.

Ideally dd.conf will support variables: BBB_HOST and BBB_API_SECRET, which in turn should be used to setup moodle and nextcloud accordingly.

While there, link documentation to how people can create their own BBB.

As a good starting point, see:

• https://gitlab.com/MaadiX/bbb-tuning/-/tree/cdist#bbb-customisation-with-the-cdist-type
• https://git.sr.ht/~evilham/cdist-evilham/tree/main/item/type/__evilham_bbb/man.rst