Rewrite of debops.gitlab_ci_runner role

'debops.gitlab_ci_runner' role has been redesigned to remove most
annoyances related to role upkeep and make it less dependent on other
roles.

This version is not compatible with previous version, I suggest
that you stop your current GitLab CI Runner installation, remove the
old files from '/srv/users/gitlab-ci-runner/' directory and reinstall
the role. Or, recreate the host from scratch.

Most important changes:

- Runner's home directory has been moved to
  '/var/local/gitlab-ci-runner/'. It can also be changed from role
  defaults if needed.

- dependencies on PostgreSQL, MySQL, NodeJS and Ansible roles have been
  dropped. Instead, role will configure different external services
  "blindly", which allows for greater flexibility - for example, MySQL
  database can now be stored on a remote host instead of just on
  localhost.

- application code cloning from git repository has been updated and role
  now better handles detached worktree used to deploy the code to
  a separate application directory.

- all role tasks have been converted from inline syntax to YAML syntax.