Update root path / to return 200

[libby]

When creating a Kubernetes Ingress for tessera the base path / for third party API returns a 404 instead of 200, which causes Ingress implementations to think the service is down. Ingress load balancers use the root path / as the health check.

At this time, there is no apparent way to set a different health check without implementation specific work.
kubernetes/ingress-nginx#3993
kubernetes/ingress-gce#42

This was discovered while trying to add Ingress routes for tessera third party API Consensys/qubernetes#27

Updating the root path / to return 200 would support generic K8s Ingress which expose the Tessera third party API as a load balanced route via Kubernetes.