Add kappa to remaining kernels

[NoraLoose]

kappa_w, kappa_s, implemented for IrregularLaplacianWithLandMask in #28, allow for spatially varying filter scale and anisotropy.

These kappa's could also be added to the following kernels:

• POPTripolarLaplacianTpoint
• MOM5LaplacianT
• MOM5LaplacianU

The remaining kernels are "simple" fixed factor Laplacians (see Section 2.6., Grooms et al. (2021), in review), which assume that the filter scale varies with the grid scale. These remaining kernels are therefore not flexible enough to get user-specified kappa's.

[jbusecke]

Is this within scope for the JOSS paper, or something that should be on the roadmap after?

[NoraLoose]

I think this is not critical, so we don't need to add it to the JOSS project. It will be pretty straightforward to do, though.