Auto-remove non-managerial participants from Tasks and Discussions when unassigned from Submission

[Hafsa-Naeem]

Description:
When a non-managerial user is unassigned from a submission, they should also be automatically removed as a participant from:

• related Tasks

• related Discussions

This keeps task/discussion participants in sync with submission assignments and prevents stale access.

What application are you using?
OJS 3.6.0

[Hafsa-Naeem]

@Vitaliy-1 Ready for review
pkp-lib: #12368
ojs: pkp/ojs#5358

[Vitaliy-1]

@Hafsa-Naeem, I see that tests are still failing:

fatal: remote error: upload-pack: not our ref 668df838fd27271e3d8746c554686ee719de57e5
fatal: Fetched in submodule path 'lib/pkp', but it did not contain 668df838fd27271e3d8746c554686ee719de57e5. Direct fetching of that commit failed.