Adds process linear_scale_range

[lforesta]

in the client the process stretch_colors was correctly deprecated in favor of linear_scale_range, but this one was not present.

[soxofaan]

minor note: this linear_scale_range(self, inputMin, inputMax, outputMin, outputMax) does not follow the standard python code style convention of using under_scores instead of dromedaryCase for variables and arguments. It should be something like

def linear_scale_range(self, input_min, input_max, output_min, output_max) -> 'ImageCollection':

[soxofaan]

I can quickly fix it myself, unless you want to do it @lforesta

[lforesta]

ah yes, I actually copy-pasted that from the openeo-processes specification, please @soxofaan feel free to change that, thanks! I'll try to remember that in case of other PRs :)