Sagemaker endpoint capability to inject boto3 client for cross account scenarios (#10728)

- **Description: Allow to inject boto3 client for Cross account access
type of scenarios in using Sagemaker Endpoint **
  - **Issue:#10634 #10184** 
  - **Dependencies: None** 
  - **Tag maintainer:** 
  - **Twitter handle:lethargicoder**

Co-authored-by: Vikram(VS) <vssht@amazon.com>

libs/langchain/langchain/llms/sagemaker_endpoint.py

@@ -80,6 +80,22 @@ class SagemakerEndpoint(LLM):
     """
 
     """
+    Args:        
+
+        region_name: The aws region e.g., `us-west-2`.
+            Fallsback to AWS_DEFAULT_REGION env variable
+            or region specified in ~/.aws/config.
+
+        credentials_profile_name: The name of the profile in the ~/.aws/credentials
+            or ~/.aws/config files, which has either access keys or role information
+            specified. If not specified, the default credential profile or, if on an
+            EC2 instance, credentials from IMDS will be used.
+
+        client: boto3 client for Sagemaker Endpoint
+
+        content_handler: Implementation for model specific LLMContentHandler 
+
+
     Example:
         .. code-block:: python
 
@@ -98,8 +114,21 @@ class SagemakerEndpoint(LLM):
                 region_name=region_name,
                 credentials_profile_name=credentials_profile_name
             )
+
+        #Use with boto3 client
+            client = boto3.client(
+                        "sagemaker-runtime",
+                        region_name=region_name
+                    )
+
+            se = SagemakerEndpoint(
+                endpoint_name=endpoint_name,
+                client=client
+            )
+
     """
-    client: Any  #: :meta private:
+    client: Any = None
+    """Boto3 client for sagemaker runtime"""
 
     endpoint_name: str = ""
     """The name of the endpoint from the deployed Sagemaker model.
@@ -157,6 +186,10 @@ class SagemakerEndpoint(LLM):
 
     @root_validator()
     def validate_environment(cls, values: Dict) -> Dict:
+        """Dont do anything if client provided externally"""
+        if values.get("client") is not None:
+            return values
+
         """Validate that AWS credentials to and python package exists in environment."""
         try:
             import boto3