Initially we support both postgres and sqlite.  See db/README.md for
many details.  Automatic migrations prior to service start are supported,
but disabled by default.  Migration status check is enabled by default,
and if status is not OK, service startup will abort.  Migration status
check can be disabled, but obviously this is not recommended.  GORM
auto migration config param is renamed to avoid confusion; using it is
not at all recommended.

NB: `atlas` is available in the image, but `go` is not.  This means that
`atlas` can only operate on the migration dir contents and the target
database (e.g., it cannot utilize its dev-url database approach to test
and dynamically plan migrations.  Therefore, auto migration only works
if the target database is clean and the sequence of pending migrations
applies directly and cleanly from the migrations dir.