Optional 'drape_input' in pygmt.Figure.grdview

An idea: add a `drape_input=` option `pygmt.Figure.grdview()` -- this relates to the discussions in https://github.com/GenericMappingTools/gmt/issues/5631. Perhaps something like `drape_red=`, `drape_green=` and `drape_blue=` which should eventually be mutually exclusive with `drape_input=`.

A general comment: GMT is super-nice! Yet one thing I find hard is its non-declarative names of options and flags and else. In my humble view, fully spelling out names of options, parametes and flags and else, is best towards human-readable code.