update the job rules templates to enable jobs on push and MRs

Relates to #54 (closed).

Previously we went to some length to disable jobs using the common job rules from running in push pipelines if there is an open MR. As noted in #54 (closed), this is sub-optimal since the Auto DevOps container scanning jobs, etc only run in push pipelines.

As such, let the upstream user of the jobs decide on their own workflow rules policy because they are the best placed to decide if they care about Auto DevOps jobs.

Add a reasonable default workflow rule to the common pipeline.