chore: Adding unit tests for Milvus and OpenAI compatibility (#2640)

# What does this PR do?
- Enabling Unit tests for Milvus to start to test OpenAI compatibility
and fixing a few bugs.
- Also fixed an inconsistency in the Milvus config between remote and
inline.
- Added pymilvus to extras for testing in CI

I'm going to refactor this later to include the other inline providers
so that we can catch issues sooner.

I have another PR where I've been testing to find other bugs in the
implementation (and required changes drafted here:
https://github.com/meta-llama/llama-stack/pull/2617).

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->

---------

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

llama_stack/providers/inline/vector_io/milvus/config.py

@@ -6,7 +6,7 @@
 
 from typing import Any
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 from llama_stack.providers.utils.kvstore.config import (
     KVStoreConfig,
@@ -19,6 +19,7 @@ from llama_stack.schema_utils import json_schema_type
 class MilvusVectorIOConfig(BaseModel):
     db_path: str
     kvstore: KVStoreConfig
+    consistency_level: str = Field(description="The consistency level of the Milvus server", default="Strong")
 
     @classmethod
     def sample_run_config(cls, __distro_dir__: str, **kwargs: Any) -> dict[str, Any]: