Do not ask for registration token if runner token is specified

What does this MR do?

When a glrt- prefixed runner token is specified in --token, it should follow the same workflow as if the token had been passed in --registration-token argument and just use that value.

Why was this MR needed?

There is a bug in the logic which causes the runner to ask for a registration token when it already has a runner token.

What's the best way to test this MR?

• Create an instance runner in the GDK through the admin UI (making sure that the new flow is available using the create_runner_workflow_for_admin FF);
• Use the register command displayed by the UI to register the runner (make sure to pass --token instead of --registration-token - the UI still needs to be updated)

With the new logic, the runner should ask for the URL, name, and executor, but not ask for the registration token.

What are the relevant issue numbers?

#30841 (closed)