add Makefile targets for fix-whitespace

[geekosaur]

make whitespace now runs fix-whitespace --check --verbose and make fix-whitespace runs fix-whitespace --verbose. You will need to install fix-whitespace yourself, but that's just a cabal install away.

This is another step in the direction of fixing #10263.

Template B: This PR does not modify behaviour or interface

E.g. the PR only touches documentation or tests, does refactorings, etc.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[Kleidukos]

Fantastic

[ulysses4ever]

I wish any new target in the makefile came with two things:

1. Update to documentation (probably, CONTRIBUTING.md) mentioning the target. It helps visibility.

2. Update to CI so that CI exercises the target. It helps avoid bit-rotting.

[Kleidukos]

This is a reasonable request yes