Metabase: We shouldn't make a user pick a DB if they only have a single one

[mazameli]

This is what it looks like currently, but we could just "auto-select" the DB for them and show the list of schemas in the DB if there are any, and if not, just show the list of tables within the DB.

[kdoh]

:+1:

[salsakran]

This doesn't seem like it needs any design, so I'm going to label it "designed"

[tlrobinson]

Just a note to remind us to update the query builder tutorial when we do this. We'll need a way to skip the db selection step if they haven't added any other databases.