Set up canary for ai-assisted webservice

There is no canary deployment for the ai-assisted webservice. During this incident we had a bad failure in that deployment that only surfaced in main stage, and then required a lengthy rollback.

We should fix this.

1. Introduce deployment in k8s-workloads
2. Introduce backend + routing in haproxy

This ticket was created from INC-3802 and was automatically exported by incident.io 🔥