reconcile the default (non-active) values of soil%watr

[har917]

The soil parameter %watr (which I understand to be a GW science parameter) is being initialised in various places through the code to differing values. At least the following exist

• 0.05 in src/coupled/ESM1.5/CABLEfilesFromESM1.5/allocate_soil_params_cbl.F90
• 0.0, 0.01, 0.02+clay, and 0.05 in cable_parameters
• 0.05 in cable_define_types
• 0.05 and 0.001 in cbl_um_init_soil (AM3)
• 0.001 in cable_um_init_subrs (ESM1.6)

This needs sorting otherwise we will end up inadvertently using the wrong value at some point and/or forgetting to keep each of these instances in sync with each other.