Add the postgres version to the schema cache

[psteinroe]

We need the postgres version in the schema cache to eg show hints or compute lints based on the version of postgres.

Note that we can copy the sql from the pg-meta library: https://github.com/supabase/postgres-meta/tree/master/src/lib/sql

[harshit54]

Hey @psteinroe , can you please checkout this pull request for the issue?

#141