Have GitLab Runner package installation ignore skel when creating user home directory

Overview

We allow users to install GitLab Runner using a package repository, which creates a home directory and has the defaults skeleton directory specified in the machine. Debian buster breaks this because of the .bash_logout (issue #4449 (closed)). In !1523 (closed) we added a flag GITLAB_RUNNER_DISABLE_SKEL which allows user to remove the skel and have the home directory empty for the gitlab-runner user.

This flag is turned off by default for now to prevent breaking change.

Proposal

• Turn on GITLAB_RUNNER_DISABLE_SKEL by default in %14.0 to prevent issues like this ever happening, if the user wants to have the skel generate they have to pass the flag explicitly.
• Update the package repository to stop mentioning the SKEL that it's on by default