Support triggering on Prime BSI and BSI Express

[aliddell]

Triggering support was omitted on #5. In order to say we "support triggering", we need to demonstrate we can do the following at a minimum:

• Query line metadata.
• Configure triggering.
• Execute software trigger.

Ideally we would like to test with hardware triggers as well, but that may be beyond the scope of this work.

[jacopoabramo]

I would like to provide some support for this feature. I have a Photometrics Kinetix (see #23 ) which I want to use in my setup together with triggers in order to achieve concurrent synchronized acquisition with a secondary camera. Where can I start looking at the source code to adapt? I can't start work immediatly and I'll probably postpone it to next year but during winter vacation I have time to kill to have a look at the code and understand it. We can also talk on Zulip if necessary.

I think I also have one or two Prime BSI in my lab but I have to double check.