feat: support tab-completion for table names in psql

Cargo.lock

Cargo.toml

src/pgproto/backend.rs

src/pgproto/backend/describe.rs

src/pgproto/backend/pgproc.rs

src/pgproto/backend/well_known_queries.rs

src/pgproto/client/extended_query.rs

src/pgproto/client/simple_query.rs

test/int/test_pgproto.py

test/pgproto/tabcompletion_test.py