Add traefik support

[kerkmann]

For traefik it's important that the ingressClassName is traefik. Tested it and it's working on with that changes. :)

[CLAassistant]

All committers have signed the CLA.

[davidzhao]

this looks good! could you update the docs in the sample config as well? that'll let others know about traefik support

[kerkmann]

Thanks for the feedback, I've added it. I hope that's enough, feel free to ask for changes. :)