Move maintenance of happy and happy-lib to @sgraf812 (#7520)

[sgraf812]

CC @andreasabel.

Fixes #7520

Checklist:

• (recommended) Package have been verified to work with the latest nightly snapshot, e.g by running the verify-package script

The script runs virtually the following commands in a clean directory:

  stack unpack $package-$version # `-$version` is optional
  cd $package-$version
  rm -f stack.yaml && stack init --resolver nightly --ignore-subdirs
  stack build --resolver nightly --haddock --test --bench --no-run-benchmarks

[mihaimaruseac]

Let's do this now and then remove the bound. Thank you