Support to create shards_num in milvus vectorstores (#20318)

To support number of the shards for the collection to create in milvus
vvectorstores.

Thank you for contributing to LangChain!

- [ ] **PR title**: "package: description"
- Where "package" is whichever of langchain, community, core,
experimental, etc. is being modified. Use "docs: ..." for purely docs
changes, "templates: ..." for template changes, "infra: ..." for CI
changes.
  - Example: "community: add foobar LLM"


- [ ] **PR message**: ***Delete this entire checklist*** and replace
with
    - **Description:** a description of the change
    - **Issue:** the issue # it fixes, if applicable
    - **Dependencies:** any dependencies required for this change
- **Twitter handle:** if your PR gets announced, and you'd like a
mention, we'll gladly shout you out!


- [ ] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [ ] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

Additional guidelines:
- Make sure optional dependencies are imported within a function.
- Please do not add dependencies to pyproject.toml files (even optional
ones) unless they are required for unit tests.
- Most PRs should not touch more than one package.
- Changes should be backwards compatible.
- If you are adding something to community, do not re-import it in
langchain.

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, hwchase17.

libs/community/langchain_community/vectorstores/milvus.py

@@ -133,6 +133,7 @@ class Milvus(VectorStore):
         partition_names: Optional[list] = None,
         replica_number: int = 1,
         timeout: Optional[float] = None,
+        num_shards: Optional[int] = None,
     ):
         """Initialize the Milvus vector store."""
         try:
@@ -191,6 +192,7 @@ class Milvus(VectorStore):
         self.partition_names = partition_names
         self.replica_number = replica_number
         self.timeout = timeout
+        self.num_shards = num_shards
 
         # Create the connection to the server
         if connection_args is None:
@@ -381,6 +383,7 @@ class Milvus(VectorStore):
                 schema=schema,
                 consistency_level=self.consistency_level,
                 using=self.alias,
+                num_shards=self.num_shards,
             )
             # Set the collection properties if they exist
             if self.collection_properties is not None: