This creates a jinja-init image based on
https://github.com/ObjectifLibre/jinja-init
We can use this image as an "init container" in k8s to template out
config files using configmaps and secrets.
It also adds a gitea-init Dockerfile, which will require the
jinja-init image to be published first.
Change-Id: I88e14c4f0d868f99aa0a0316e6b9e24c2a8fea68
83237bc01e