DPL-nnn Migrate all script/runners to step_planners

[JamesGlover]

Describe the Housekeeping
Script/runners have some significant performance overheads, as they involve spinning up an entirely new process, and rely on serialization and deserialization of their information, which often results in excess database queries.

Note: Care will have to be made to avoid affecting any global state, as global state will be shared by all jobs.

Long term we could consider performing some tasks synchronously as well.

Blocking issues
Describe any other issues or tickets that may be blocking this change.

Additional context
Add any other context about the problem here.