docs: Add docs for Upstash Vector built-in embeddings support (#7485)

Co-authored-by: Jacob Lee <[email protected]>

docs/core_docs/docs/integrations/vectorstores/upstash.ipynb

@@ -64,6 +64,14 @@
         "\n",
         "You can create an index from the [Upstash Console](https://console.upstash.com/login). For further reference, see [the official docs](https://upstash.com/docs/vector/overall/getstarted).\n",
         "\n",
+        "Upstash vector also has built in embedding support. Which means you can use it directly without the need for an additional embedding model. Check the [embedding models documentation](https://upstash.com/docs/vector/features/embeddingmodels) for more details.\n",
+        "\n",
+        "```{=mdx}\n",
+        ":::note\n",
+        "To use the built-in Upstash embeddings, you'll need to select an embedding model when creating the index.\n",
+        ":::\n",
+        "```\n",
+        "\n",
         "### Credentials\n",
         "\n",
         "Once you've set up an index, set the following environment variables:\n",
@@ -127,6 +135,38 @@
         "});"
       ]
     },
+    {
+      "cell_type": "markdown",
+      "id": "afa53a9c",
+      "metadata": {},
+      "source": [
+        "## Usage with built-in embeddings\n",
+        "\n",
+        "To use the built-in Upstash embeddings, you can pass a `FakeEmbeddings` instance to the `UpstashVectorStore` constructor. This will make the `UpstashVectorStore` use the built-in embeddings, which you selected when creating the index."
+      ]
+    },
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "id": "cbabe6f7",
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "import { UpstashVectorStore } from \"@langchain/community/vectorstores/upstash\";\n",
+        "import { FakeEmbeddings } from \"@langchain/core/utils/testing\";\n",
+        "\n",
+        "import { Index } from \"@upstash/vector\";\n",
+        "\n",
+        "const indexWithEmbeddings = new Index({\n",
+        "  url: process.env.UPSTASH_VECTOR_REST_URL,\n",
+        "  token: process.env.UPSTASH_VECTOR_REST_TOKEN,\n",
+        "});\n",
+        "\n",
+        "const vectorStore = new UpstashVectorStore(new FakeEmbeddings(), {\n",
+        "  index: indexWithEmbeddings,\n",
+        "});"
+      ]
+    },
     {
       "cell_type": "markdown",
       "id": "ac6071d4",
@@ -360,4 +400,4 @@
   },
   "nbformat": 4,
   "nbformat_minor": 5
-}
+}