Implement basic metadata filtering in Qdrant (#1689)

This PR implements a basic metadata filtering mechanism similar to the
ones in Chroma and Pinecone. It still cannot express complex conditions,
as there are no operators, but some users requested to have that feature
available.

tests/integration_tests/vectorstores/test_qdrant.py

@@ -56,6 +56,20 @@ def test_qdrant_with_metadatas(
     assert output == [Document(page_content="foo", metadata={"page": 0})]
 
 
+def test_qdrant_similarity_search_filters() -> None:
+    """Test end to end construction and search."""
+    texts = ["foo", "bar", "baz"]
+    metadatas = [{"page": i} for i in range(len(texts))]
+    docsearch = Qdrant.from_texts(
+        texts,
+        FakeEmbeddings(),
+        metadatas=metadatas,
+        host="localhost",
+    )
+    output = docsearch.similarity_search("foo", k=1, filter={"page": 1})
+    assert output == [Document(page_content="bar", metadata={"page": 1})]
+
+
 @pytest.mark.parametrize(
     ["content_payload_key", "metadata_payload_key"],
     [