Move vector stores to own package

[marcusschiesser]

Start with 'postgres' package.

1. Move DocumentStore, KVStore and VectorStore to their own postgres package in providers/storage (and other pg deps if they exist)
2. Test with supabase and add pooling support like VercelPool if available

[fire015]

Settings.embedModel would need to be transitioned over to the new package.

[marcusschiesser]

We're having now also a dedicated postgres package: #1597