ci: enable OBS rebuild on push for the 'obs' branch

Note that this is not enabled in main, but needs to be there
otherwise the webhook fails on push to main instead of being
a no-op

Author: bluca

.obs/workflows.yml

@@ -0,0 +1,13 @@
+rebuild:
+  steps:
+    - trigger_services:
+        project: system:systemd
+        package: particleos-debian
+    - trigger_services:
+        project: system:systemd
+        package: particleos-fedora
+  filters:
+    event: push
+    branches:
+      only:
+        - obs