Method SoftDeleteAsync(IEnumerable<long>, IRedbUser, long?)

Mark objects for soft-deletion with explicit user.
Creates a trash container and moves objects and their descendants under it.
Actual deletion happens in background via IBackgroundDeletionService.

public Task<DeletionMark> SoftDeleteAsync(IEnumerable<long> objectIds, IRedbUser user, long? trashParentId = null)