Use different branch prefix for mintmaker updates

As we are using konlux branch to pull upload changes from upstream, we
need to use a different branch for mintmaker.
Also update the schedule, so that it doesn't just run on weekends.

Author: yuumasato

renovate.json

@@ -0,0 +1,4 @@
+{
+    "branchPrefix": "kflux/mintmaker/",
+    "schedule": ["at any time"]
+}