Add support for gitlab omnibus containers/pod

[dkerwin]

Add support for gitlab omnibus containers/pod (https://docs.gitlab.com/omnibus/README.html).

Example events:

Shell spawned in a container other than entrypoint (user=<NA> k8s_gitlab.XXX (id=YYYY) shell=sh parent=sshd cmdline=sh -c /opt/gitlab/embedded/service/gitlab-shell/bin/gitlab-shell key-42)

Shell spawned in a container other than entrypoint (user=<NA> k8s_gitlab.XXX (id=YYY) shell=sh parent=git cmdline=sh -c git-upload-pack '/var/opt/gitlab/git-data/repositories/example/demo_service.git' git-upload-pack '/var/opt/gitlab/git-data/repositories/example/demo_service.git')

Might make sense to create a bunch of dedicated gitlab rules as my approach is pretty generic.

[mstemm]

Thanks for the improvements!