citemplate: tweak merge-request rules

With the MergeRequest rules template, its was impossible to manually create or trigger a pipeline for a branch/commit that was not part of a merge request.

This tweaks the workflow:rules such that there will always be a pipeline for each commit (which will be set to a manual job trigger).

There is the downside that we will now be triggering 2 pipelines in case of merge requests, but they will require manual action to be started.