Add allowed_run_types parameter to Dag class

[eladkal]

Body

Some workflows are designed to be purely automatic. We should allow the capability for DAG author to declare DAG as scheduled run only. This means:

1. Create manual run button from the UI will generate error / be disabled.
2. Create manual run from API will generate error.
3. Scheduler will not run tasks of manual DagRuns if the parameter is set.

To allow flexibility I'm proposing the allowed_run_types should be enum ['Scheduled', 'Backfill', 'Manual'] where user choose what to set. Thus we need to define the set of allowed rules per type.

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.