Improve cleanup task executions older than x days to include those with no start / end timestamp

[klopfdreh]

Problem description:
Currently it is not possible to include task executions to delete in which the start / end timestamp has not been set while using "Cleanup older execution(s)" - because of this all executions that have this state need to be removed manually.

Solution description:
Add a checkbox beside "Only completed execution(s)" and "Cleanup oder execution(s)" that allow to also cleanup those which have no start / end timestamp

Description of alternatives:
N/A

Additional context:
N/A