feat: add redisearch vectorstore (#1307)

# Description

Add `RediSearch` vectorstore for LangChain

RediSearch: [RediSearch quick
start](https://redis.io/docs/stack/search/quick_start/)

# How to use

```
from langchain.vectorstores.redisearch import RediSearch

rds = RediSearch.from_documents(docs, embeddings,redisearch_url="redis://localhost:6379")
```

tests/integration_tests/vectorstores/test_redis.py

@@ -0,0 +1,26 @@
+"""Test Redis functionality."""
+
+from langchain.docstore.document import Document
+from langchain.vectorstores.redis import Redis
+from tests.integration_tests.vectorstores.fake_embeddings import FakeEmbeddings
+
+
+def test_redis() -> None:
+    """Test end to end construction and search."""
+    texts = ["foo", "bar", "baz"]
+    docsearch = Redis.from_texts(
+        texts, FakeEmbeddings(), redis_url="redis://localhost:6379"
+    )
+    output = docsearch.similarity_search("foo", k=1)
+    assert output == [Document(page_content="foo")]
+
+
+def test_redis_new_vector() -> None:
+    """Test adding a new document"""
+    texts = ["foo", "bar", "baz"]
+    docsearch = Redis.from_texts(
+        texts, FakeEmbeddings(), redis_url="redis://localhost:6379"
+    )
+    docsearch.add_texts(["foo"])
+    output = docsearch.similarity_search("foo", k=2)
+    assert output == [Document(page_content="foo"), Document(page_content="foo")]