Supply a helm chart

[FrederikNJS]

What would you like to be added:
I would like to have a helm chart for easily installing and updating Agola on Kubernetes.

Why is this needed:
Installing and updating Agola is somewhat cumbersome, due to it only supplying an example configuration for installing on Kubernetes. If Agola changes the example configuration in the future, diffing and modifying the configuration your own configurations will be hard.

[xeruf]

I concur - and then it would be good to also be able to configure OAuth2 providers in the ConfigMap.

[babykart]

I recently published the helm chart that I'm actually using : https://github.com/babykart/agola-helm
This helm chart deploys agola in the distributed mode only.
When the agola team integrate its own helm chart, I will remove mine.