Replace anaphoric `with-source-and-dest-dbs` with hygienic alternative (#38175)

Closes https://github.com/metabase/metabase/issues/36103

### Description

This change introduces a new `with-dbs` macro which is hygienic and supports an arbitrary number of databases.

For now I am leaving the old `with-source-and-dest-dbs` macro, so we can deal with the noise of upgrading the tests in a later PR. I upgrade a single test so that the usage is clear.