add semantic cache index

Author: Jibola

langchain-python/indexes/langchain_test_index_semantic_cache.json

@@ -0,0 +1,18 @@
+{
+    "fields": [
+        {
+            "numDimensions": 1536,
+            "path": "embedding",
+            "similarity": "cosine",
+            "type": "vector"
+        },
+        {
+            "path": "llm_string",
+            "type": "filter"
+        }
+    ],
+    "name": "langchain-test-index-semantic-cache",
+    "type": "vectorSearch",
+    "database": "langchain_test_db",
+    "collectionName": "langchain_test_cache"
+}