Stimulus epoch generation for multiplane ophys sessions

**Is your feature request related to a problem? Please describe.**
Stimulus epochs are generated for ephys using the camstim module. This module has been extended to multiplane but requires some changes for the session json to be valid. I would like to use the branch ophys-stim-epochs-and-fov and create a PR into stage-ophys-session-july-4 to resolve the features required to be compliant. Once the stim-epochs of the session json is complete and the code is cleaned up, I can work on the unit tests and submit a PR from stage-ophys-session-july4 into main.