Allow configuring options for each server entry

[julianvmodesto]

For all server entries in the HAProxy config, I would like to manage maxconn.

For example:

  server pod-100.103.160.82 100.103.160.82:8080 maxconn 1000
  server pod-100.112.130.212 100.112.130.212:8080 maxconn 1000

This would be possible if we allowed templating or adding options to the server directive.

[tamalsaha]

We were planning to support this via annotations on pod. This will be similar to how the backend weight works currently.

Also related #491 (limit-* annotations)

[tamalsaha]

Example:
ingress.appscode.com/max-connections: 3000

If applied on Ingress, this will be set as the global maxconn

If applied to Pod (via Deployment, etc), this will be on the server line like backend weight.

[tamalsaha]

limit-rps* - Rate limiting: http://www.haproxy.com/blog/use-a-load-balancer-as-a-first-row-of-defense-against-ddos/