Move kubernetes-entrypoint to init-container

[fwiesel]

Personally, I like the approach openstack/openstack-helm to move the kubernetes-entrypoint to the init-container.

This way, we do not have to add the executable to the image, and we can use a minimal kubernetes-entrypoint container to fulfil the same purpose.

[Kuckkuck]

but keep in mind, that there is still a bug open, init containers are not executed when a node was rebooted. kubernetes/kubernetes#36485

[fwiesel]

That's a bit annoying. Then we have to postpone that, until that issue has been closed.