Design routine to expose on blue-red arm synchronously

For one channel, ics_spsaitActor design was quite simple because we were obviously controlling one ccd and one shutter.

But as SM1 is coming soon and we need, at minimum, to synchronise blue and red arm.
The user will be able to choose between either blue, red or both arms.

That said, as fmadec mentionned in INSTRM-193, we can't expose on blue arm without exposing the red one. We'll need to be careful in that case