CNG: Parameterize the version of exiftool

Summary

With a specific exiftool version in use, we should parameterize that as we have with other software version controls.

Details

The following discussion from [external] should be addressed:

• @WarheadsSE started a discussion:

  We can split the following work into future MRs, to continue with this MR quickly:

  • Add EXIFTOOL_VERSION to ci_files/variables.yml
  • Update .gitlab-ci.yml to pass the additional argument in the gitlab-ruby jobs.