ingress: Enable controller.allowSnippetAnnotations

Set controller.allowSnippetAnnotations to true since Reggie uses
such a snippet.

This is to deal with the following error I encountered when trying to update Reggie in the staging cluster:

Error: cannot patch "reggie" with kind Ingress: admission webhook  
"validate.nginx.ingress.kubernetes.io" denied the request:  
nginx.ingress.kubernetes.io/server-snippet annotation cannot be  
used. Snippet directives are disabled by the Ingress administrator