CI/CD template for ccache builds

Inspired by https://twitter.com/kmdouglass/status/1048868727813562368?s=12.

We can make it easy for users to implement builds based on ccache optimization to speed up the process. It seems that we could benefit from it for our internal flow: omnibus-gitlab#3460 (closed)

The MVC could be a gitlab-ci.yml template people can customize and reuse.

(This feature is part of https://gitlab.com/gitlab-org/gitlab-ce/issues/21624 but there was no proposal so far)