[kubernetes-ingress] Support for adding SPOA container to IC deployment

[mecampbellsoup]

In HAProxy there is a nice extension of the protocol called Stream Processing Offload Protocol:

https://www.haproxy.com/blog/extending-haproxy-with-the-stream-processing-offload-engine
https://github.com/haproxy/haproxy/blob/master/doc/SPOE.txt

It is intended to be a fast, non-blocking way of extending HAProxy functionality without having to patch the HAProxy source code directly. Instead you can communicate over a TCP connection with a "microservice".

Is there any support currently for marrying our HAProxy pod(s) to the new SPOA pod(s) that we want to deploy?

I asked similar/related questions in the IC repo but opening an issue here since it feels like more of a Helm chart/template feature:

• Feature request: additional backends e.g. for haproxy spoa kubernetes-ingress#449
• Configure spoa filter kubernetes-ingress#357

[dkorunic]

Additional background information for now: https://www.mail-archive.com/haproxy@formilux.org/msg44680.html