fixed index name error found at redis new vector test (#2311)

This PR fixes a logic error in the Redis VectorStore class
Creating a redis vector store `from_texts` creates 1:1 mapping between
the object and its respected index, created in the function. The index
will index only documents adhering to the `doc:{index_name}` prefix.
Calling `add_texts` should use the same prefix, unless stated otherwise
in `keys` dictionary, and not create a new random uuid.

langchain/vectorstores/redis.py

@@ -69,7 +69,7 @@ class Redis(VectorStore):
         ids = []
         # Check if index exists
         for i, text in enumerate(texts):
-            _key = keys[i] if keys else uuid.uuid4().hex
+            _key = keys[i] if keys else self.index_name
             key = f"{prefix}:{_key}"
             metadata = metadatas[i] if metadatas else {}
             self.client.hset(