What this PR does / why we need it:

Two small additions to how the Milvus online store treats a collection that already exists, both
behind settings that are off by default.

Schema check. A collection's schema only applies when Feast creates it. Until now Feast used an
existing collection as it was, so a feature view that gained a field, lost a field or changed its
vector dimension failed later with a Milvus error at write or read time, or kept writing into a
stale schema. Feast now compares the fields of an existing collection with the schema the feature
view declares, the first time a process touches the collection and on every feast apply. By
default it logs a warning that names each difference, as it already does for a missing partition key. With
fail_on_schema_mismatch: true it raises a ValueError instead, so the mismatch is caught at
feast apply. Field types are not compared, because reads and writes adapt to the types a
collection has. The Redis, Postgres and SQLite online stores do not have this problem: a feature is
a hash field or a row there, so a changed feature view needs no schema change.

Mutation timeout. PyMilvus retries a failed upsert or delete and, without a timeout, a call can
wait for a long time, for example while a cluster refuses writes at its memory quota. Streaming
writers need a bound so a stuck call fails and the batch can be retried. mutation_timeout is
passed as the PyMilvus timeout of every upsert and delete. PyMilvus applies it to each attempt
and stops retrying once the elapsed time exceeds it, so a call ends within the timeout plus one
attempt. When unset, nothing is sent and PyMilvus keeps its default retry policy. The Redis online store takes the same control from socket_timeout and
socket_connect_timeout in its connection_string.

online_store:
  type: milvus
  fail_on_schema_mismatch: true
  mutation_timeout: 60

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): a missing field, an extra field and a changed vector dimension are logged,
  or raised with fail_on_schema_mismatch, and the placeholder vector of older collections is
  ignored; an invalid mutation_timeout is rejected by the config.

• Unit (Milvus Lite): a changed feature view applied again by the same process warns, then
  raises with the setting; timeout is sent to upserts and deletes only when mutation_timeout is set.

• Server: the schema check raises on a real collection; writes and deletes with a timeout succeed.

Unit tests run on Milvus Lite 3.2.1 (pymilvus 3.0.2). The server tests in
sdk/python/tests/integration/online_store/test_milvus_remote.py pass against a local Milvus
3.0.2 server. The existing Milvus unit and server tests pass unchanged.

Misc

Follows #7082, #7083 and #7084, which brought the Milvus online store the row deletion, partition
options and write-batch ordering that the Redis online store has, and Simon Hearne's series #6882,
#6895, #6917, #6921 and #6940.