Ability to add prefixes and suffixes to implied names in vtk export

Currently, the functions `write_solution` accepts the arg `suffix` to append to the field name when exporting. However, `write_cellset` does not provide this option.

A more consistent way to handle this would be to have
```julia
Ferrite.write_solution(vtk, dh, a; prefix = "", suffix = "")
Ferrite.write_cellset(vtk, grid; prefix = "", suffix = "")
Ferrite.write_facetset(vtk, grid; prefix = "", suffix = "")
Ferrite.write_nodeset(vtk, grid; prefix = "", suffix = "")
```
for all cases. This can be achieved without any breaking API, and IMO the keyword args make this easier to work with than the current `suffix` arg in `write_solution`, but that would of course remain supported for backwards compatibility.

This interface would also resolve the discussion [here](https://github.com/Ferrite-FEM/Ferrite.jl/pull/1303#discussion_r2924775866).