Add feature view versioning support to MongoDB online store

## Summary

Add versioned feature view read/write support to the `MongoDB` 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/mongodb_online_store/mongodb.py`

## Related

Part of #2728