Add again optional GAP3 package

[stumpc5]

We have been trying to have an optional GAP3 package for a while now. Franco then made one (#8906) but it contained binaries, so it was removed again (#19164).

We now know how to make the package work for linux, but osx seems to be a problem.

• Download GAP3 from ​https://webusers.imj-prg.fr/~jean.michel/gap3/ (make sure with Jean Michel that this version is up-to-date)
• Get rid of the binaries in

  bin
  pkg/anusq/bin/Sq
  pkg/arep/bin/desauto
  pkg/arep/bin/leonin
  pkg/arep/bin/leonout
  pkg/meataxe/tests/a1
  pkg/meataxe/tests/a2
  pkg/meataxe/tests/Perm1
  pkg/meataxe/tests/Perm2
  pkg/nq/bin/nq
  pkg/sisyphos/bin/sis-i586-unknown-linux
  pkg/ve/bin/me
  pkg/ve/bin/qme
  

  (Jean sent me that list, needs to be checked.)
• Write the code to compile GAP3 from source and put it into the right place.