Rename fastscape parameter

[anne-glerum]

This PR changes the name of an input parameter that describes the "transport coefficient" or "diffusivity" kd when selecting additional FastScape output. At the moment, it is called "deposition coefficient", which is actually the name of the parameter G, as also used in fastscape.cc, e.g.:

            bedrock_deposition_g = prm.get_double("Bedrock deposition coefficient");
            sediment_deposition_g = prm.get_double("Sediment deposition coefficient");

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[gassmoeller]

Code looks good and the renaming makes sense.

How long has this parameter been in the code? If it was added before the last release: Please add a changelog entry that describes the renaming. Ideally we would also include it in the list of updated parameters in our update script, see here, is this possible, or is it too confusing with the other deposition coefficient parameters?

[anne-glerum]

The PR that introduced this parameter (#6504) was merged Jun 19, 2025, so after the latest release.

I'll try adding the renaming to the update script.

[anne-glerum]

Renaming has been added to the update script.

[gassmoeller]

Very nice, thanks!