add option to write output of BeamSpotMon as json file

Part of prototype to include InteractionRegion calibration within Alignment task.

Adds functionality to BeamSpotMonitor to write out information necessary to calculate InteractionRegion calibration to json file.

Required for Alignment!715 (merged) MooreOnline!654 (merged)

the work here relies on and borrows heavily from @spradlin's work on BeamSpotMon