fix #526: adding support for search_path_db

[joaocc]

Proposal of implementation of for a search_path_db to allow setting search path by database for each user
fixes #526

Code generated via Cursor Composer + Claude 3.7 Sonnet, but not tested

[Speeddymon]

I think this would be useful, but it could be improved by being a nested block instead of a map type attribute, because you could then use the dynamic qualifier on the block to iterate over the databases independently. For example if you want to for_each a postgresql_role resource, then as this is written it would be more complex to give each role different DB level search paths whereas if it were instead a nested block, then it would be simpler.