Implement ability to parse JSON payload from /runners/verify
What does this MR do?
This MR changes VerifyRunner to be able to parse a JSON payload (same as the one returned from RegisterRunner) that will start being returned from GitLab %15.10 and later.
Why was this MR needed?
In order to support the writing of the runner data in config.toml that is not available locally.
What's the best way to test this MR?
Test the expected behavior of verifying a runner against an old (<15.10) and a new GitLab instance. For the new GitLab instance, you'd need a local GDK, so I can run the tests locally and post the results here. The idea is that old Runners should be able to talk to new GitLab instances, and inversely, new Runners should be able to talk to old GitLab instances (although they won't get the new registration flow).