Provide a standard list of variables for toggling

### What problem does your feature request solve?

Typing in field names is a laborious process, fraught with the the risk of typos. and frustrated with the inadequacy of rose edit's lists.

### Describe the solution you'd like

Provide a pre-populated list of common fields that can be toggled on or off. This could just be specific field names, or it could be more general concepts that maps to both UM and LFRic field names. An option should be provided for manual input to deal with rare or custom fields however.

### Describe alternatives you've considered

Maybe a seperate ticket, but it would be useful to provide different lists to different models, even when they use the same recipe, to allow of UM vs. LFRic comparisons.

### Questions

Is there a standard set of model variables?

Start by locating how CSET currently accepts and toggles field names, then compare that flow with the existing Rose Edit lists and the UM and LFRic naming conventions mentioned in the issue. Define what a standard variable set and model-specific mapping should contain before implementing anything. Done means common fields can be selected without typing while rare or custom fields remain manually configurable.

Written by the indexing model from the issue text.