Better handle ISIS Camera Version information attachment

Currently if there is no information in ["IsisCube"]["Kernels"]["CameraVersion"] in the incoming label, ALE fails [here](https://github.com/USGS-Astrogeology/ale/blob/306a6d8429ceed24952e375e13be13aa945e19a5/ale/base/label_isis.py#L72) and ISIS handles the spiceinit. However, since Camera Version is ISIS camera version information, I don't think failing is the proper way to handle this because no raw mission EDR label will have this information.

Looking into how ISIS handles this, it seems spiceinit calls CameraFactory::CamerVersion [here](https://github.com/USGS-Astrogeology/ISIS3/blob/bea365e49480a74620a8ae69171a143d316a28f7/isis/src/base/apps/spiceinit/spiceinit.cpp#L451) which looks for a Camera plugin file (either local or at location $ISISROOT/lib/Camera.plugin) to inform the ISIS camera version.

We could duplicate this logic, since ALE is typically used WITH ISIS we could assume this plugin file exists exactly the same as ISIS does? I am really curious to hear other's thought because I am not well versed in ALE big picture architecture.