Add the go version of the registration tests that were initially written in python

What does this MR do?

Adds native (go) tests for exercising the runner binary's register command. These were previously written in a different project in Python: https://gitlab.com/erushton/runner-registration-tests/

Why was this MR needed?

Because no one can deal with Python and they weren't being exercised when living outside the main pipeline.

What's the best way to test this MR?

⚠ Need to add a step that grabs/builds a copy of the runner locally on the same job.

What are the relevant issue numbers?

#27267 (closed)