Substring support for similarity_search_with_score (#10746)

**Description:** Possible to filter with substrings in
similarity_search_with_score, for example: filter={'user_id':
{'substring': 'user'}}

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/langchain/langchain/vectorstores/pgembedding.py

@@ -360,6 +360,13 @@ class PGEmbedding(VectorStore):
                             value_case_insensitive[IN]
                         )
                         filter_clauses.append(filter_by_metadata)
+                    elif isinstance(value, dict) and "substring" in map(
+                        str.lower, value
+                    ):
+                        filter_by_metadata = EmbeddingStore.cmetadata[key].astext.ilike(
+                            f"%{value['substring']}%"
+                        )
+                        filter_clauses.append(filter_by_metadata)
                     else:
                         filter_by_metadata = EmbeddingStore.cmetadata[
                             key