feat: add private weaviate api_key support on from_texts (#3139)

This PR adds support for providing a Weaviate API Key to the VectorStore
methods `from_documents` and `from_texts`. With this addition, users can
authenticate to Weaviate and make requests to private Weaviate servers
when using these methods.

## Motivation
Currently, LangChain's VectorStore methods do not provide a way to
authenticate to Weaviate. This limits the functionality of the library
and makes it more difficult for users to take advantage of Weaviate's
features.

This PR addresses this issue by adding support for providing a Weaviate
API Key as extra parameter used in the `from_texts` method.

## Contributing Guidelines
I have read the [contributing
guidelines](https://github.com/hwchase17/langchain/blob/72b7d76d79b0e187426787616d96257b64292119/.github/CONTRIBUTING.md)
and the PR code passes the following tests:

- [x] make format
- [x] make lint
- [x] make coverage
- [x] make test

langchain/vectorstores/weaviate.py

@@ -25,6 +25,35 @@ def _default_schema(index_name: str) -> Dict:
     }
 
 
+def _create_weaviate_client(**kwargs: Any) -> Any:
+    client = kwargs.get("client")
+
+    if client is not None:
+        return client
+
+    weaviate_url = get_from_dict_or_env(kwargs, "weaviate_url", "WEAVIATE_URL")
+    weaviate_api_key = get_from_dict_or_env(
+        kwargs, "weaviate_api_key", "WEAVIATE_API_KEY", None
+    )
+
+    try:
+        import weaviate
+    except ImportError:
+        raise ValueError(
+            "Could not import weaviate python  package. "
+            "Please install it with `pip instal weaviate-client`"
+        )
+
+    auth = (
+        weaviate.auth.AuthApiKey(api_key=weaviate_api_key)
+        if weaviate_api_key is not None
+        else None
+    )
+    client = weaviate.Client(weaviate_url, auth_client_secret=auth)
+
+    return client
+
+
 class Weaviate(VectorStore):
     """Wrapper around Weaviate vector database.
 
@@ -248,18 +277,11 @@ class Weaviate(VectorStore):
                     weaviate_url="http://localhost:8080"
                 )
         """
-        weaviate_url = get_from_dict_or_env(kwargs, "weaviate_url", "WEAVIATE_URL")
 
-        try:
-            from weaviate import Client
-            from weaviate.util import get_valid_uuid
-        except ImportError:
-            raise ValueError(
-                "Could not import weaviate python  package. "
-                "Please install it with `pip instal weaviate-client`"
-            )
+        client = _create_weaviate_client(**kwargs)
+
+        from weaviate.util import get_valid_uuid
 
-        client = Client(weaviate_url)
         index_name = kwargs.get("index_name", f"LangChain_{uuid4().hex}")
         embeddings = embedding.embed_documents(texts) if embedding else None
         text_key = "text"