What this PR does / why we need it:

Adds two optional Milvus online store settings, each Strong, Bounded, Session or Eventually:

• consistency_level is sent with every read and search (query, search, keyword query).
• collection_consistency_level is set when Feast creates a collection. It becomes the collection's
  default for requests that don't specify a level, e.g. from other clients.

The two are independent. When they are unset nothing is sent, so Milvus keeps its default
(Bounded), which is the current behaviour.

With Bounded, a read issued straight after materialization may briefly miss the newest writes.
consistency_level: Strong makes Feast's reads always see the latest writes, at the cost of higher
read latency, and takes effect without recreating collections.

online_store:
  type: milvus
  consistency_level: "Strong"
  collection_consistency_level: "Bounded"

Which issue(s) this PR fixes:

N/A

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests

• Integration tests

• Manual tests

• Testing is not required for this change

• Unit (mocked client): neither level sent when unset; consistency_level sent only to query,
  search and keyword query; collection_consistency_level sent only to create_collection;
  different values for each are applied independently; invalid values rejected.

• Server: collection level is Bounded by default and follows collection_consistency_level;
  with consistency_level: Strong on a Bounded collection, a write is visible to the next read.

Unit tests run on Milvus Lite 3.2.1 (pymilvus 3.0.2). Server tests in sdk/python/tests/integration/online_store/test_milvus_remote.py are marked integration and skip unless ZILLIZ_URI and ZILLIZ_TOKEN are set; they passed against a local Milvus 2.6.0, a local Milvus 3.0.2 server and against Zilliz Cloud. The existing Milvus unit and universal integration tests pass unchanged.

Misc

Part of a series of Milvus online store improvements for Zilliz Cloud and production Milvus, following #6882, #6895 and #6917.