Update SageMaker Endpoint Embeddings docs to be up to date with current requirements (#8103)

- **Description:** Simple change of the Class that ContentHandler
inherits from. To create an object of type SagemakerEndpointEmbeddings,
the property content_handler must be of type EmbeddingsContentHandler
not ContentHandlerBase anymore,
  - **Twitter handle:** @Juanjo_Torres11

Co-authored-by: Bagatur <baskaryan@gmail.com>

docs/extras/integrations/text_embedding/sagemaker-endpoint.ipynb

@@ -39,11 +39,11 @@
    "source": [
     "from typing import Dict, List\n",
     "from langchain.embeddings import SagemakerEndpointEmbeddings\n",
-    "from langchain.llms.sagemaker_endpoint import ContentHandlerBase\n",
+    "from langchain.embeddings.sagemaker_endpoint import EmbeddingsContentHandler\n",
     "import json\n",
     "\n",
     "\n",
-    "class ContentHandler(ContentHandlerBase):\n",
+    "class ContentHandler(EmbeddingsContentHandler):\n",
     "    content_type = \"application/json\"\n",
     "    accepts = \"application/json\"\n",
     "\n",