gitlab-ci: Move changelog linting logic to shell script

Allowing it to be easily used locally.
23 jobs for master
Status Job ID Name Coverage
  Lint
canceled #219659
lint
lint-linters

canceled #219662
lint
lint-submods-branch

canceled #219660
lint
lint-testsuite

canceled #219661
lint
typecheck-testsuite

 
  Quick Build
canceled #219663
x86_64-linux
hadrian-ghc-in-ghci

 
  Build
canceled #219666
x86_64-linux
release-x86_64-linux-deb9

canceled #219665
x86_64-linux
validate-x86_64-linux-deb9-debug

canceled #219667
x86_64-linux
validate-x86_64-linux-deb9-dwarf

canceled #219664
x86_64-linux
validate-x86_64-linux-deb9-hadrian

 
  Full Build
canceled #219670
aarch64-linux allowed to fail
validate-aarch64-linux-deb9

canceled #219671
armv7-linux allowed to fail
validate-armv7-linux-deb9

canceled #219672
x86_64-linux
validate-i386-linux-deb9

canceled #219669
x86_64-darwin
validate-x86_64-darwin

canceled #219673
x86_64-linux
validate-x86_64-linux-deb9-integer-simple

canceled #219668
x86_64-linux
validate-x86_64-linux-deb9-unreg-hadrian

canceled #219674
x86_64-linux
validate-x86_64-linux-fedora27

canceled #219676
x86_64-windows allowed to fail
validate-x86_64-windows

canceled #219675
x86_64-windows allowed to fail
validate-x86_64-windows-hadrian

 
  Cleanup
canceled #219677
x86_64-darwin
cleanup-darwin

 
  Packaging
canceled #219678
x86_64-linux allowed to fail
doc-tarball

 
  Testing
canceled #219679
x86_64-linux allowed to fail manual
hackage

canceled #219680
x86_64-linux
perf-nofib

 
  Deploy
canceled #219681
x86_64-linux allowed to fail
pages