Reuse credential template from argocd and github app authentication

[BeyerJC]

When using the PullRequest generator for example, i can pass a tokenRef to authenticate my Github enterprise repositories.

Since applicationset is now bundles with argocd , i think it would be great if the could reuse credential templates that are created in argo.

Currently im using Github App for authentication and it would be great if i could use the same method for applicationset, ideally reuse the existing one!