Supported custom ernie_api_base for Ernie (langchain-ai#10416)

Description: Supported custom ernie_api_base for Ernie
 - ernie_api_base：Support Ernie custom endpoints
 - Rectifying omitted code modifications. langchain-ai#10398

Issue: None
Dependencies: None
Tag maintainer: @baskaryan 
Twitter handle: @JohnMai95

libs/langchain/langchain/chat_models/ernie.py

@@ -56,6 +56,9 @@ class ErnieBotChat(BaseChatModel):
 
     """
 
+    ernie_api_base: Optional[str] = None
+    """Baidu application custom endpoints"""
+
     ernie_client_id: Optional[str] = None
     """Baidu application client id"""
 
@@ -84,6 +87,9 @@ class ErnieBotChat(BaseChatModel):
 
     @root_validator()
     def validate_environment(cls, values: Dict) -> Dict:
+        values["ernie_api_base"] = get_from_dict_or_env(
+            values, "ernie_api_base", "ERNIE_API_BASE", "https://aip.baidubce.com"
+        )
         values["ernie_client_id"] = get_from_dict_or_env(
             values,
             "ernie_client_id",
@@ -97,7 +103,7 @@ def validate_environment(cls, values: Dict) -> Dict:
         return values
 
     def _chat(self, payload: object) -> dict:
-        base_url = "https://aip.baidubce.com/rpc/2.0/ai_custom/v1/wenxinworkshop/chat"
+        base_url = f"{self.ernie_api_base}/rpc/2.0/ai_custom/v1/wenxinworkshop/chat"
         model_paths = {
             "ERNIE-Bot-turbo": "eb-instant",
             "ERNIE-Bot": "completions",
@@ -125,7 +131,7 @@ def _chat(self, payload: object) -> dict:
     def _refresh_access_token_with_lock(self) -> None:
         with self._lock:
             logger.debug("Refreshing access token")
-            base_url: str = "https://aip.baidubce.com/oauth/2.0/token"
+            base_url: str = f"{self.ernie_api_base}/oauth/2.0/token"
             resp = requests.post(
                 base_url,
                 timeout=10,

libs/langchain/langchain/embeddings/ernie.py

@@ -61,7 +61,7 @@ def _embedding(self, json: object) -> dict:
     def _refresh_access_token_with_lock(self) -> None:
         with self._lock:
             logger.debug("Refreshing access token")
-            base_url: str = "https://aip.baidubce.com/oauth/2.0/token"
+            base_url: str = f"{self.ernie_api_base}/oauth/2.0/token"
             resp = requests.post(
                 base_url,
                 headers={