chore: split DAL into two packages, with moduleconfig queries moved to common/configuration

[deniseli]

Fixes #1696

Approach:

• Duplicate - engine block of sqlc.yaml to support multiple out locations
• Refactor common error handling vars + funcs into separate dalerrs package. This now lives under the new top level db dir, where we can add additional common DB logic as we split the controller dal further. This change incurred a lot of NOOP lines changed. :/
• Meat of the change: split moduleconfig CRUD queries out of backend/controller/sql and into common/configuration/sql. Correspondingly, split the moduleconfig DAL functions out of backend/controller/dal and into common/configuration/dal.
• Questionable choice: Copied backend/controller/sql/conn.go to common/configuration/sql/conn.go with the unnecessary logic stripped out (Tx...). That means that what remains (sql.DBI and sql.NewDB), though a small amount of code, is duplicated with the original conn.go. I could refactor this to use a shared interface instead, but that could also make this messier for readability and take things in a worse direction overall, so pending better ideas, we can rethink this when splitting the controller DAL.

[alecthomas]

This is awesome! I'm keen to start splitting it up further, it'll make the code a lot cleaner.