ENH: Regional differences in KdU parameters

[MImmesberger]

Is your feature request related to a problem?

This is just for future reference because this came up a couple of times (and recently @MartinWiegandecon asked me about it): Currently we use placeholder values for the maximum rent per m2 and maximum apartment size in m2. In fact, these parameters differ across municipalities (maximum rent per m2) and across Bundesländer (apartment size).

Describe the solution you would like to see

Choose (empirical) averages for the parameters.

Supporting variation across municipalities

@MartinWiegandecon sent me this overview for 2024. However, finding out which parameters were used by the municipalities in the past is not trivial (if possible at all).