Default diagnostic: T_sfc instead of canopy temperature in default diagnostics

[AlexisRenchon]

T_sfc is defined everywhere whereas t_canopy is set to NaN if there is no canopy

Note, this is stored in p.T_sfc and currently not in define_diagnostics.jl for the land model (but it is for the bucket).

for the bucket:

    # Bucket Surface temperature
    add_diagnostic_variable!(
        short_name = "tsfc",
        long_name = "Bucket Surface Temperature",
        standard_name = "surface_temperature",
        units = "K",
        comments = "Temperature of the bucket-land surface.",
        compute! = (out, Y, p, t) ->
            compute_surface_temperature!(out, Y, p, t, land_model),
    )

Question: Do we need a separate short_name for the land model?