Provide mechanism to update Ingress's status when running in external mode

[asoc]

Currently HAproxy ingress only updates an Ingress's status when --publish-service is used, however when running in external mode there is no Service to point to. Some applications I've run across require the status to be updated before doing certain operations, so they're effectively broken until something can be done to update them.

Proposed options:

• --publish-address=a.b.c.d,my.domain specify the exact IP(s) and/or domain to use
• --publish-interface=eth0 lookup the IP address on the given interface(s) and use that