docs: Standardize QianfanEmbeddingsEndpoint (langchain-ai#24786)

- **Description:** Standardize QianfanEmbeddingsEndpoint, include:
  - docstrings, the issue langchain-ai#21983 
  - model init arg names, the issue langchain-ai#20085

Author: maang-h

libs/community/langchain_community/embeddings/baidu_qianfan_endpoint.py

@@ -11,12 +11,45 @@
 
 
 class QianfanEmbeddingsEndpoint(BaseModel, Embeddings):
-    """`Baidu Qianfan Embeddings` embedding models."""
+    """Baidu Qianfan Embeddings embedding models.
 
-    qianfan_ak: Optional[SecretStr] = None
+    Setup:
+        To use, you should have the ``qianfan`` python package installed, and set
+        environment variables ``QIANFAN_AK``, ``QIANFAN_SK``.
+
+        .. code-block:: bash
+
+            pip install qianfan
+            export QIANFAN_AK="your-api-key"
+            export QIANFAN_SK="your-secret_key"
+
+    Instantiate:
+        .. code-block:: python
+
+            from langchain_community.embeddings import QianfanEmbeddingsEndpoint
+
+            embeddings = QianfanEmbeddingsEndpoint()
+
+     Embed:
+        .. code-block:: python
+
+            # embed the documents
+            vectors = embeddings.embed_documents([text1, text2, ...])
+
+            # embed the query
+            vectors = embeddings.embed_query(text)
+
+            # embed the documents with async
+            vectors = await embeddings.aembed_documents([text1, text2, ...])
+
+            # embed the query with async
+            vectors = await embeddings.aembed_query(text)
+    """  # noqa: E501
+
+    qianfan_ak: Optional[SecretStr] = Field(default=None, alias="api_key")
     """Qianfan application apikey"""
 
-    qianfan_sk: Optional[SecretStr] = None
+    qianfan_sk: Optional[SecretStr] = Field(default=None, alias="secret_key")
     """Qianfan application secretkey"""
 
     chunk_size: int = 16

libs/community/tests/integration_tests/embeddings/test_qianfan_endpoint.py

@@ -1,5 +1,9 @@
 """Test Baidu Qianfan Embedding Endpoint."""
 
+from typing import cast
+
+from langchain_core.pydantic_v1 import SecretStr
+
 from langchain_community.embeddings.baidu_qianfan_endpoint import (
     QianfanEmbeddingsEndpoint,
 )
@@ -38,3 +42,17 @@ def test_rate_limit() -> None:
     assert len(output) == 2
     assert len(output[0]) == 384
     assert len(output[1]) == 384
+
+
+def test_initialization_with_alias() -> None:
+    """Test qianfan embedding model initialization with alias."""
+    api_key = "your-api-key"
+    secret_key = "your-secret-key"
+
+    embeddings = QianfanEmbeddingsEndpoint(  # type: ignore[arg-type, call-arg]
+        api_key=api_key,  # type: ignore[arg-type]
+        secret_key=secret_key,  # type: ignore[arg-type]
+    )
+
+    assert cast(SecretStr, embeddings.qianfan_ak).get_secret_value() == api_key
+    assert cast(SecretStr, embeddings.qianfan_sk).get_secret_value() == secret_key