Add option to set a configurable default ingressclass for ingresses

[oyvindio]

It could be useful to be able to set a default ingressclass for ingress resources managed by fiaas-deploy-daemon via the kubernetes.io/ingress.class annotation.

When moving to the networking.k8s.io/v1 ingress API (#40) it becomes possible to tag a IngressClass resource as the default at the cluster level. Even with this option, it could still be useful to have the ability to have a (different) default configured at the fiaas-deploy-daemon instance level. (When moving to the v1 ingress API, fiaas-deploy-daemon default ingress class should likely be implemented via the ingressClass field and not the annotation)