Improvements of install script and macos-installhs-cabal new azure job

[jneira]

• Add job to test the build of install.hs with macos and cabal
• Improvements over install.hs:
  • Remove unused imports
  • Pass number of jobs and verbosity shake args to build tools
  • Use custom cabal.project-${ghcVersion} if exists
  • I added cabal.project-ghc-8.8.2 that will be used by the script
  • Add comments with the possible resolvers to shake.yaml

I am not sure about the "pass number of jobs and verbosity shake args to build tools". It is a cheap way to let users control the number of jobs and verbosity but they are shared between the run of the script itself and the calls to build tools.

Fixes some warts described in #1664

[jneira]

Finally i removed the sharing between the jobs arg of shake and the build tool: the output of shake with more than one job was interleaved and, in general, we will want different values of jobs for shake and stack/cabal frequently.

[jneira]

My mistake was mix azure and install changes so the pr is bigger than necessary

[jneira]

Well all ci is green (including install.hs jobs) and some changes are needed to make easier ghc-8.8.3 support, so i am gonna merge it