Record source of pausing inbound queue.

[jatgarg]

Please note that there are many players who can pause op processing:

1. DeltaScheduler
2. ScheduleManager
3. Summarizer
4. Container (code proposal)

Given that API is generic and is available to all layers, more users may show up later.

From @vladsud
Add a system to track who's pausing ops, and a way to expose first/last/maybe all actors who caused ops to sit paused

• I'd suggest for pause() to take some token (string, better - assert tag, clearly representing call site) and return another token (coutner). And for resume() to require token returned from pause() to match them and keep tracking who keeps queue paused. That would give us full picture and enforcement that pause() & resume are properly paired (and if not - we always know the offender)
• A simpler system might be for resume() to accept token (like assert tag) to clearly articulate who was the last one to resume op processing, and thus we can log it with duration. This is less powerful system, but much simpler to implement for this task.

Originally posted by @vladsud in #8912 (comment)

[jatgarg]

workitem=491