Update documentation to include operational management of DB

[ghost]

There’s a bit of sparse information on deploying MAAS and initially connecting it to a database (external or internal), but what’s missing, is the operational management of the DB itself, covering topics such as “How do I reconfigure MAAS to point to a new DB DSN/IP address?”, and “How do I perform DB maintenance, while bringing up a secondary/failover/DR site?” and similar.

Support engineers: David Desrosiers, Adam Vest

(Duplicates https://warthogs.atlassian.net/browse/MAASENG-1796)

[evilnick]

@billwear is this something you have looked at?

[billwear]

there are two things you should do next: (1) please go to the "Features" section of the doc discourse and describe what you want, so that not only myself but also the MAAS engineers can see it; and (2) please give a much more detailed explanation of what you want to be created: "and similar" is too vague.