Run deploy_dashboards on master only

In 96adfd9c, the 3 rules are removed which led to them running on scheduled jobs as !reference [".default-job-rules", rules] was not added for deploy_dashboards. But in !5643 (comment 1341188734), the wrong rules were referenced, creating a new set of problems.

This mr rectifies the original problem correctly by introducing .default-job-rules which DRYs up

- *avoid-stage-group-check-rule
- *avoid-downstream-generation-pipelines-rule
- *avoid-schedule-rule