What this PR does / why we need it:

#7120 added native ARRAY and JSON columns to the Milvus online store, behind
enable_openai_compatible_store. This PR removes that condition. Every new collection stores
arrays and Json values natively:

enable_openai_compatible_store keeps its original meaning: it selects native numeric columns.
Map and Struct stay serialized, as in #7120.

Why no flag. The text storage is not a format to keep. A filter cannot reach a base64 column,
and Milvus cannot validate it. With the flag, a user gets the weaker storage unless they find a
setting whose name does not describe it. The #7120 benchmark shows that native columns cost nothing
on insert and make array and JSON path filters possible.

Effect on existing users. A collection that an older Feast version created keeps its VARCHAR
columns and keeps working. The column types of each collection decide how a row is written and
read, as #7025 does for numeric columns. Only new collections change, and three things differ for
them:

• An array holds at most 4096 elements.
• A Json value must be an object or an array.
• JSON text comes back re-serialized, so its formatting can change.

The docs describe how to recreate a collection and a staged cutover that avoids a feast teardown.

Open question for maintainers. Is a new default with a release note acceptable here? If you
prefer to keep an opt-in flag, I will close this PR, or change it to a dedicated flag with a
clearer name.

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): Json and arrays get nullable JSON and ARRAY columns with the flag
  off, and numerics stay VARCHAR until the flag is on.

• Unit (Milvus Lite): the complex-value round-trip, the JSON path filter and the array element
  delete from feat: Add native complex types and scalar index tags to the Milvus online store #7120 now run with the default config.

• Server: the same tests pass on a local Milvus 3.0.2 server without the flag.

76 unit tests on Milvus Lite 3.2.1 (pymilvus 3.0.2) and 15 server tests in
sdk/python/tests/integration/online_store/test_milvus_remote.py pass.

Misc

Follows #7120. This PR and #7118 change adjacent lines of the config table in the docs. I will
rebase the second one after the first merges.