Allow opt out of SNI ALB

[mikkeloscar]

#111 added support for aggregating ingresses with different Certificates under a single ALB using SNI.

Some clients might not support SNI and thus we should support opting out of an SNI ALB and create an a single ALB per certificate like before.

I suggest we do this with an annotation on the ingress object.

Something like:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: myingress
  annotations:
    zalando.org/aws-load-balancer-sni: false

https://en.wikipedia.org/wiki/Server_Name_Indication

[szuecs]

It might makes sense to opt-out globally per flag, too