Add option to have sensitive planes

[THanae]

It would be good to have the option to add sensitive planes in the geometry. This could potentially be added as a "sub-detector", with several shapes (either a plane or a cylinder, the latter being useful for studies around the target).
To make use cases clearer, planes which are already used in FairShip could be implemented, with the option to have additional planes as needed?

[olantwin]

I wonder whether this would be better to add to geometry_service or aegir. We generally need to think about more how we want to define sensitive detectors across components.

I have examples with sensitive planes in the geometry for my fixed-target geometry, but realise that I never shared them...

[matclim]

I would put this in aegir as per the discussion last Friday. I am therefore closing this issue and reopening it there.

[olantwin]

Thanks!

Note for the next time, one can transfer issues between repos, maintaining their comments, history etc.