Implement relation filtering on get_catalog macro

[mikealfare]

resolves #900

Problem

When get_catalog runs, it needs to return all relations within a schema, hence it cannot be parallelized or scale. It also means that all relations will be returned, not just those managed by dbt.

Solution

Allow for a set of relations to be passed in to limit the query against the database.

• add _get_one_catalog_relations method
• point _get_one_catalog to this method since the second half is the same
• register that this capability is available

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[mikealfare]

This was the second half of _get_one_catalog above. It is broken out as it's own method now so it can be reused by the new method _get_one_catalog_by_relations below.

[mikealfare]

There is no method on RelationsCache that returns a specific BaseRelation. The next best option is to constantly return the set of relations in a schema (RelationsCache.get_relations) and then look for the target relation in that set. This method duplicates the logic in get_relations and adds the third check on identifier.