Switch to new changelog generator

See https://github.com/vector-im/element-web/pull/18370 / https://github.com/matrix-org/matrix-react-sdk/pull/6537 / https://github.com/matrix-org/matrix-js-sdk/pull/1824

release_config.yaml

@@ -1 +1,7 @@
 signing_id: releases@riot.im
+subprojects:
+    element-web:
+        includeByDefault: true
+        # Because element-web is not in our dependencies, but the versions
+        # follow those of this project (well, vice-versa really)
+        mirrorVersion: true