Trigger build every 7 days at 05:00 and allow rebuild trigger

.github/workflows/image.yml

@@ -1,6 +1,9 @@
 name: Build Bredbandskollen's CLI docker image
 
 on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 5 * * */7"
   push:
     branches: master