Call API to create runner (1)

What does this MR do and why?

This MR depends on !110593 (merged)

This change adds an API call to create a runner using then new workflow.

The result is meant to redirect the user to a registration page.

Related MRs

Add CreateRunner Mutation Endpoint (!110593 - merged)
Call API to create runner (1) (!111789 - merged)	👈 you are here
Add runner registration instructions (2) (!112487 - merged)
Add installation command for drawer (3) (!112561 - merged)

Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag: in your console rails c, and then Feature.enable(:create_runner_workflow)
2. Visit Admin -> CI/CD -> Runners
3. Select the "New instance runner" button
4. Input values to create a new runner
5. After "submit", confirm the success message
6. In the runner list a "Never connected" runner will appear.

When we continue work on the registration page, users will be able to register their runners in this page.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #383139 (closed)