Upload CI/CD secrets to GitHub

This is a nice to have.

When the app is created, it comes with a nice CI/CD config which requires 4 secrets (prod and staging namespace and auth). The first thing to do to finish the setup is to find those 4 secrets somewhere in the Console (not obvious) and paste them in the GitHub Secrets store. This is well documented but could be automated for a greater developer experience!

### Expected Behaviour
Secrets are created for me once the GitHub url is known.

### Actual Behaviour
I have to first find the secrets (not obvious) and copy / paste them in GitHub.

cc @meryllblanchet

Start by reading the generator's CI/CD configuration and the setup flow that knows the GitHub URL; trace how the four production and staging namespace and auth secrets are currently obtained from the Console. Done means the required GitHub Secrets are created automatically once the GitHub URL is known, without manual copying.

Written by the indexing model from the issue text.