fix: postgres metadata filters (#11927)

docs/examples/vector_stores/postgres.ipynb

llama-index-core/llama_index/core/vector_stores/types.py

...tores-postgres/llama_index/vector_stores/postgres/base.py

..._stores/llama-index-vector-stores-postgres/pyproject.toml

...llama-index-vector-stores-postgres/tests/test_postgres.py