Document the REST API used by runners
Description
I want to understand more about how the runner communicates with the gitlab server and be able to write alternative runners using this information.
Proposal
If it is at all possible it would be very useful to have an OpenAPI 3.0 spec for the runner API. Or at least a documented record of the calls the server supports for runners. This would open the door wider to community supported runners (I am considering writing a runner for a system where I have zero hope of using Go)
Links to related issues and merge requests / references
https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.0.md