Finish the GitLab Runner role

[gregharvey]

This role currently (optionally) manages config for Fargate runners but not for other types. We can at least support shell runners and some of the options available in a standard config file, which we already have as variables so it's misleading.

We also need to be able to set multiple configs and services for multiple runners, as it's entirely possible you will want either or both of different users running different runners (i.e. different services) and multiple runners under the same user.