fsapp: implement app.inspect based iter_active

[pmrowla]

Currently we implement iter_queued and iter_processed for manually accessing tasks as raw messages via the FS kombu broker. (This is needed for when there is no worker process running, since celery.control.inspect requires talking to a worker via broadcast messages)

dvc-task/src/dvc_task/app/filesystem.py

Lines 123 to 130 in 5a49fbe

	def iter_processed(
	self, queue: Optional[str] = None
	) -> Generator[Message, None, None]:
	"""Iterate over tasks which have been taken by a worker.
	Arguments:
	queue: Optional name of queue.
	"""

Ideally we should also have an inspect-based wrapper which can return actual active tasks via celery.inspect for use when we have an active worker process