Adding heptio/contour support

[cmaloney]

I'm currently using https://github.com/heptio/contour inside the organization where I work, with kube-lego to get letsencyrpt certificates. This largely works (projectcontour/contour#106 (comment) describes the caveats), and the "nginx" mode more or less applies / works out of the box with kube-lego, however the ingress created by kube-lego specifically sets the ingress class tag to "nginx", and does a full rewrite of the ingress definition regularly (so just hand-editing the class tag to "contour" is ineffective to keep things working).

I'd like to help contribute towards making kube-lego work out of the box with contour, although need some guidance on how to make that happen / work best.

[simonswine]

The latest canary of kube-lego should support the provider ingress option. I would give a to set the class to contour and the provider to nginx and see what happens:

kubernetes.io/ingress.provider: nginx
kubernetes.io/ingress.class: contour