Add feature view versioning support to PostgreSQL online store #6168

Summary

Add versioned feature view read/write support to the PostgreSQL online store, so that version-qualified feature references (e.g., driver_stats@v2:trips_today) resolve to the correct versioned data.

Context

Feature view versioning was introduced in #6101. Currently, only the SQLite online store supports versioned reads/writes. All other online stores raise VersionedOnlineReadNotSupported when a versioned ref is used.

The implementation pattern (see sqlite.py for reference) involves:

1. Write path: When enable_online_feature_view_versioning is enabled, materialize data into a version-specific table/key namespace (e.g., {project}_{fv_name}_v{version})
2. Read path: Route version-qualified lookups to the correct versioned table/key namespace

Reference implementation

• SQLite online store: sdk/python/feast/infra/online_stores/sqlite.py
• Store file: sdk/python/feast/infra/online_stores/postgres_online_store/postgres.py

Related

Part of #2728