[Command] authgear database migrate up error message improvement

When I provided a schema name that doesn't exist in the db, it shows `no schema has been selected to create in` (in fact I input the wrong db name). And I really think I use the wrong argument name or something. Can it change to message like `schema doesn't exist in db`? (I know this message comes from psql though :()

Start with the `authgear database migrate up` command and reproduce the failure using a nonexistent schema or database name. Trace where the psql error is surfaced, then make the message distinguish an invalid database or schema; done means the command reports the correct cause instead of `no schema has been selected to create in`.

Written by the indexing model from the issue text.