Postgres: Add support for schemas containing special characters

[alfredringstad]

As stated in #445, the MigrationsTableExists function does not properly query when the schema contains special characters, since it is then querying for the quoted value.

This PR makes it use unquoted values instead, and adds tests for this behaviour (the tests will fail on the current main branch).

[gregwebs]

awesome, thank you for the contribution!
@dossy let's get this merged.

[dossy]

Nice, this looks good.

While I think we can merge this PR as-is, I would love to see three more test cases, where drv.migrationsTableName is set to a schema.tablename where schema contains a character that would require quoting in one case, tablename contains a character that would require quoting in another case, and where both schema and tablename contain characters that require quoting in the third case. I fully expect the code to pass these additional tests as-is, so it's not essential to have the tests, but it would be nice.

This is purely for completeness, and like I said, I think this PR can definitely be merged as-is, but if @alfredringstad agrees and adds these three additional tests, I would be happy to wait on merging until they're added.

[alfredringstad]

Thanks! ☺️

[mijamo]

Hello! Would it be possible to get a patch release with those changes included @dossy ? I am unsure about the release process so forgive me if that was already planned

[amacneil]

Done!