Self-contained internal git repository

[manics]

devspace should have a self-hosted git repository to support running without GitHub. All jobs could push/pull from this internal git repo, and an optional separate job would push this to GitHub if required. This removes the need for a secret SSH key or github token.

[jburel]

for this training, I have removed the usage of a shared key as discussed with @sbesson and @joshmoore