Introduction of looping instruction or goto instruction

[evvaaaa]

Use Case

Currently the queueserver can be set to loop mode:

bluesky-queueserver/bluesky_queueserver/manager/plan_queue_ops.py

Lines 1634 to 1636 in 062265d

	if loop_mode:
	item_to_add = self.set_new_item_uuid(item)
	await self._add_item_to_queue(item_to_add)

This is useful, but there are other situations where my scientists want to run, for example,

1. 10 plans with differing arguments, repeating 3 times
2. A single plan to change some condition
3. Another single plan to change some condition
4. 7 plans with differing arguments, repeating 10 times
   ... and so on and so fourth with 12 hours worth of plans.

Proposal

Option 1

I propose adding two new instructions:

loop_start

{"name": "loop_start", "options": {"num": N}, "item_type": "instruction"}

Initiates a loop, the plans between this and an exit instruction will be repeated N times.

loop_exit

{"name": "loop_exit", "item_type": "instruction"}

Marks the end of the loop.

Option 2

A more general goto instruction, with some way to handle conditionals:

{"name": "goto", "options": {"absolute_index": N, "repeat_limit": M}, "item_type": "instruction"}

A running queueserver would have state for how many times each goto has been ran and skip them once repeat_limit is reached.

The following would repeat an entire queue forever:

{"name": "goto", "options": {"absolute_index": 0}, "item_type": "instruction"}

We could also allow goto to specify relative index, repeat the last two plans N times:

{"name": "goto", "options": {"relative_index": -2, "repeat_limit": N}, "item_type": "instruction"}