add scaling to LMR data

[fmaussion]

Quite niche

[fmaussion]

@pat-schmitt as part of other changes I renamed area_m2_min_h to area_min_h_m2 for consistency with other vars (all other vars have units at the end of their names). I don't think it will have dramatic consequences, thoughts on this?

[fmaussion]

Furthermore I noticed that this here is not exactly correct:

### Dynamic spinup params
# Defines the minimum ice thickness which is used during the dynamic spinup to
# match area or volume. Only grid points with a larger thickness are considered
# to the total area. This is needed to filter out area changes due to climate
# variability around the rgi year (spikes).
dynamic_spinup_min_ice_thick = 2.

In fact this is a new diagnostic for all variables as well - I'll think about how to make this consistent.

[fmaussion]

need to add length_min_h for consistency