feat: ✨ Added filtering option to FAISS vectorstore (#5966)

Inspired by the filtering capability available in ChromaDB, added the
same functionality to the FAISS vectorestore as well. Since FAISS does
not have an inbuilt method of filtering used the approach suggested in
this [thread](https://github.com/facebookresearch/faiss/issues/1079)
Langchain Issue inspiration:
https://github.com/hwchase17/langchain/issues/4572

- [x] Added filtering capability to semantic similarly and MMR
- [x] Added test cases for filtering in
`tests/integration_tests/vectorstores/test_faiss.py`

#### Who can review?

Tag maintainers/contributors who might be interested:

  VectorStores / Retrievers / Memory
  - @dev2049
  - @hwchase17

tests/integration_tests/vectorstores/test_faiss.py

@@ -74,6 +74,28 @@ def test_faiss_with_metadatas() -> None:
     assert output == [Document(page_content="foo", metadata={"page": 0})]
 
 
+def test_faiss_with_metadatas_and_filter() -> None:
+    texts = ["foo", "bar", "baz"]
+    metadatas = [{"page": i} for i in range(len(texts))]
+    docsearch = FAISS.from_texts(texts, FakeEmbeddings(), metadatas=metadatas)
+    expected_docstore = InMemoryDocstore(
+        {
+            docsearch.index_to_docstore_id[0]: Document(
+                page_content="foo", metadata={"page": 0}
+            ),
+            docsearch.index_to_docstore_id[1]: Document(
+                page_content="bar", metadata={"page": 1}
+            ),
+            docsearch.index_to_docstore_id[2]: Document(
+                page_content="baz", metadata={"page": 2}
+            ),
+        }
+    )
+    assert docsearch.docstore.__dict__ == expected_docstore.__dict__
+    output = docsearch.similarity_search("foo", k=1, filter={"page": 1})
+    assert output == []
+
+
 def test_faiss_search_not_found() -> None:
     """Test what happens when document is not found."""
     texts = ["foo", "bar", "baz"]