[ENH] Use "main" branch instead of "master" in CAE generated repositories

[pdolif]

The code-generation service creates new repositories and still names the main branch "master" instead of "main".
This should be changed, such that all the new repositories created by the CAE use the "main" branch.

Besides that, the CAE expects the CAE-Deployment-Temp repository to have a "master" branch. If new users create the deployment temp repository now, it will automatically have a "main" branch instead of "master". Then the deployment is not working.