Availability of HybridOfflineStore

There is [hybrid_offline_store.py](https://github.com/feast-dev/feast/blob/master/sdk/python/feast/infra/offline_stores/hybrid_offline_store.py) which has HybridOfflineStore. However, there is no documentation.

Please advise if this is available to create a feature view from multiple data sources.

The feature_store.yaml below can be loaded into FeatureStore. But not clear how to add Feature Views there.
```
from feast.infra.offline_stores.snowflake import (
SnowflakeSource
)
from feast.infra.offline_stores.contrib.spark_offline_store.spark import (
SparkSource
)
from feast.infra.offline_stores.hybrid_offline_store import (
HybridOfflineStore,
HybridOfflineStoreConfig
)

store = FeatureStore(
repo_path="."
)
store
-----
FeatureStore(
repo_path=PosixPath('.'),
config=RepoConfig(project='hybrid_feature_store', project_description=None, provider='local', registry_config='data/registry.db', online_config='sqlite', auth={'type': 'no_auth'}, offline_config={'type': 'feast.infra.offline_stores.hybrid_offline_store.HybridOfflineStore', 'offline_stores': [{'type': 'snowflake.offline', 'conf': {'account': '...', 'user': '...', 'role': '...', ...}}, {'type': 'spark', 'conf': {}}]}, batch_engine_config='local', feature_server=None, flags=None, repo_path=PosixPath('.'), entity_key_serialization_version=2, coerce_tz_aware=True, materialization_config=MaterializationConfig(pull_latest_features=False)),
registry=,
provider=
)
```

## features_store.yaml
```
project: hybrid_feature_store
registry: data/registry.db
provider: local

offline_store:
type: feast.infra.offline_stores.hybrid_offline_store.HybridOfflineStore
offline_stores:
- type: snowflake.offline
conf:
account: ${ACCOUNT}
user: ${USER}
role: ${ROLE}
...
- type: spark
conf: {}

entity_key_serialization_version: 2
```