Handle vertical levels generically

### What problem does your feature request solve?

There are multiple kinds of vertical levels, such as pressure or model level. This is exacerbated in LFRic world, where we also have half_levels and full_levels, and the names are different. This prevents recipes that handle vertical levels from being model agnostic.

### Describe the solution you'd like

We should have a lookup for the vertical coordinate in a cube, similar to the `get_cube_yxcoordnames` utility function. This will allow operators to correctly handle any cube without regard to the vertical levels. Then a single recipe and rose-edit entry can be added.

### Describe alternatives you've considered

Pressure should probably be handled separately, at least in rose edit, as it would be more meaningful to select specific pressure values than for other levels.