This feature installs gitlab-runner according official guide [1]

The following envs can be altered:

GL_USER - define default gitlab-runner username ('gitlab-runner' by default)
GL_SSH_KEY - ssh pubkey added to authorized_keys of GL_USER

NOTE: this feature depends on network enablement in hasher (see [2] for details)
      and mkimage [3]

1. https://docs.gitlab.com/runner/install/linux-manually.html
2. https://bugzilla.altlinux.org/34596
3. https://git.altlinux.org/people/legion/packages/mkimage.git?p=mkimage.git;a=commitdiff;h=6e90f032f15f89de1c2c523a725e369ab6cad1a0
