Add method to mark a DispositionTask as "held"

[sharonwarner]

The DispositionTask model (previously HoldHearingTask) needs to have a held method. This method should perform the following actions:

1. Confirm the task's associated hearing's disposition is 'held'. This hearing can be found through the DispositionTasks's parent (a HearingTask) which will have a HearingTaskAssociation.
2. If the appeal is a legacy appeal:
   • We complete the DispositionTask
   • The HearingTask should automatically close
   • We move the appeal to location 33 for transcription
3. If the appeal is an AMA appeal:
   • We create a TranscriptionTask as a child of the DispositionTask
   • We create an EvidenceWindowTask as a child of the DispositionTask that expires in 90 days unless the associated hearing has marked evidence_window_waived

For more information, see here: https://github.com/department-of-veterans-affairs/appeals-design-research/blob/master/Projects/Hearings/Hearing%20Schedule/Tech%20Specs/HearingTaskFlow.md

Acceptance criteria

• Add method to mark hearings as held on DispositionTasks during job that will run every night
• When a DispositionTask is marked held for a LegacyAppeal, complete that task, complete the parent task, and change the VACOLS location to 33
• When a DispositionTask is marked held for am AMA Appeal, create a child TranscriptionTask and maybe a child EvidenceWindowTask

[lowellrex]

MEDIUM. Similar to #9539.