Hardcoded ObservationalDataCollector in JSON Frontend

[christopher-wild]

Is your feature request related to a problem? Please describe.
Current implementation of the JSON frontend has the ObservationalDataCollector hardcoded into it so you have to use it.

Describe the solution you'd like
To investigate the use of other data collectors (ExperimentalDataCollector) in the Frontend.

Additional context
It would be useful to have this as a feature, however it may also be difficult / messy to implement as the ExperimentalDataCollector requires abstract methods to be implemented. The current frontend is a command line utility requiring no user written python and this would be a change to that.

[jmafoster1]

Since we've now dropped the ExperimentalDataCollector class and have a new frontend, I don't think is relevant anymore.