[postgres] Sort Ascending

[hinthornw]

Adds a few of preliminaries:

1. Makes the returned "score" actually the result of the requested operation (cosine, inner_product, l2)
2. Sorts asc, etc. so that if you were to add an HNSW index (and not have any WHERE filters), it would be used
3. Drop the inner WHERE statement if no namespace or other filters are provided. See (2) for why.
   I don't yet add an index to the migrations since I think we need to agree on the right balance to ensure it's actually used in common query patterns.