added pgvector implementation and updated doc

backend/src/main/resources/application.yaml

@@ -21,6 +21,12 @@ spring:
       api-key: ${OPENAI_KEY}
       chat:
         model: gpt-4o-mini
+    vectorstore:
+      pgvector:
+        dimensions: 1536
+        distance-type: COSINE_DISTANCE
+        index-type: HNSW
+        initialize-schema: true
   session:
     store-type: jdbc
     jdbc: