This will enable us to access the auth records, which we store in a separate database for weird legacy reasons!
We don't do anything else yet, just set up the connection to be available.
(NOTE: This commit was a bit of a history rewrite: we started working on this with `database.yml` still gitignored, but then in 8fb6e82 we added it back in to be able to fix a bug in 44c42f9. So previously this branch added back `database.yml` to git *and* added `openneo_id` to it, but since then I've rebased against the other changes, and rewrote history to make this a change to *just* add the database! I also moved it in the timeline, to be before some of the other things that depend on it.)