Add helm chart OBS proxy

Create a helm chart for deploying the server side of the obs proxy. The
main thing that needs to be configured by users here is the ingress as
well as the obs backend server. The backend server when running in
kubernetes as well should be available via <cluster ip name>.<namespace>
as the dns name as per kubernetes conventions.

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>