executor/gitlab_runner_cfg: fix valve-infra containers creation, rework the access control policy, and simplify our runner configuration
Many changes to our runner configuration, addressing some Mesa developers' concerns. Additionally, I took the opportunity to simplify our gitlab runner config and make the default template more generic.
At some point, I would like to make a copy of this default template and host it in the ansible role. This would remove the last valve-infra-specific config (the gitlab_runner_prebuild
script), but this is not really a priority right now.
These changes have been deployed in my farm and they do not impact dxvk-ci, upstream mesa, nor downstream mesa.