Community/Partner: Adding Azure community and partner user agent to better track usage in Python (#29561)

- This pull request includes various changes to add a `user_agent`
parameter to Azure OpenAI, Azure Search and Whisper in the Community and
Partner packages. This helps in identifying the source of API requests
so we can better track usage and help support the community better. I
will also be adding the user_agent to the new `langchain-azure` repo as
well.

- No issue connected or  updated dependencies. 
- Utilises existing tests and docs

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/partners/openai/langchain_openai/chat_models/azure.py

@@ -643,7 +643,10 @@ class AzureChatOpenAI(BaseChatOpenAI):
             "organization": self.openai_organization,
             "base_url": self.openai_api_base,
             "timeout": self.request_timeout,
-            "default_headers": self.default_headers,
+            "default_headers": {
+                **(self.default_headers or {}),
+                "User-Agent": "langchain-partner-python-azure-openai",
+            },
             "default_query": self.default_query,
         }
         if self.max_retries is not None:

libs/partners/openai/langchain_openai/embeddings/azure.py

@@ -198,7 +198,10 @@ class AzureOpenAIEmbeddings(OpenAIEmbeddings):  # type: ignore[override]
             "base_url": self.openai_api_base,
             "timeout": self.request_timeout,
             "max_retries": self.max_retries,
-            "default_headers": self.default_headers,
+            "default_headers": {
+                **(self.default_headers or {}),
+                "User-Agent": "langchain-partner-python-azure-openai",
+            },
             "default_query": self.default_query,
         }
         if not self.client:

libs/partners/openai/langchain_openai/llms/azure.py

@@ -153,7 +153,10 @@ class AzureOpenAI(BaseOpenAI):
             "base_url": self.openai_api_base,
             "timeout": self.request_timeout,
             "max_retries": self.max_retries,
-            "default_headers": self.default_headers,
+            "default_headers": {
+                **(self.default_headers or {}),
+                "User-Agent": "langchain-partner-python-azure-openai",
+            },
             "default_query": self.default_query,
         }
         if not self.client: