Use the search path to resolve table names in Doltgres

[zachmu]

Doltgres enables the UseSearchPath global at startup, which triggers this behavior.

This is a shim to get a proof of concept of this behavior working faster. A better solution, coming next, involves making this behavior pluggable and putting this logic in the Doltgres package, not in Dolt.

Companion PRs:

https://github.com/dolthub/go-mysql-server/pull/2498 https://github.com/dolthub/doltgresql/pull/269