[4.1] [API] Feature Request: Endpoint for workflow transition trigger events

Related and similar to the closed ticket 1043 (Your speed at addressing new tickets is surprising and deeply appreciated. I really wanted to thank the team already.)

Description:

• There are endpoints for transition fields. See mayan/apps/document_states/url.py, Line 336
• There are no endpoints for transition trigger events
• The front end handles creation and deletion of transition-trigger_events relationships with a form WorkflowTransitionTriggerEventRelationshipForm in a set WorkflowTransitionTriggerEventRelationshipFormSet. See mayan/apps/document_states/forms.py, Line 129.
• The front end handles listing trigger_events for a given transition with a html widget widget_transition_events. See mayan/apps/document_states/html_widgets.py, Line 6

Use case:

Any scenario requiring creation of a workflow through the API with event based automated transitions.

Request:

As each "event-transition" relationship is a Model and and entry in public.document_states_workflowtransitiontriggerevent, it would make sense to post/put/patch the full list of trigger_events to update the list as is done by the front end form (create & delete).

Having to send the full list to add or remove trigger events adds the need for a list getter similar to the html widget.

• POST: api/v4/workflow_templates/id/transitions/id/actions/

Either with event_type_id:
{
  event_type_ids: [1,2,...]
}
or paths
{
  event_types: ["namespace.label","namespace.label",...]
}

• GET: api/v4/workflow_templates/id/transitions/id/actions/

{
  count: 2,
  ...
  results: [ "namespace.label", "namespace.label" ]
}