k8s: deploy git server

[herzogf]

ArgoCD needs a git server to pull the argocd configs (declarative config for argocd projects and apps) as well as the configs for the applications. Applications can originate from the user or from homek8s itself for optional components, e.g. istio, knative, ...

Thus by default we need to deploy a git server in k8s (can be deactivated). Gitea seems to be an option as it is a lightweight git server: https://docs.gitea.io/en-us/comparison/