pin git submodule using https protocol

Using git/ssh protocl for submodule repo prevents us from pulling
connectorx as a cargo dependency by a specific git commit.

Author: houqp

.gitmodules

@@ -1,3 +1,4 @@
 [submodule "federated-query"]
 	path = federated-query
-	url = [email protected]:sfu-db/federated-query.git
+	url = https://github.com/sfu-db/federated-query.git
+	branch = main