feat: add /metrics endpoint to gateways

[Julusian]

• Use the HealthEndpoints helper in LSG
• Deduplicate/unify some code which is repeated across all the gateways
• Add prom-client to server-core-integration and setup a /metrics in HealthEndpoints
• Enable default nodejs metrics in the endpoint
• A first pass of some easy sofie metrics in each gateway

I believe the docker images have these ports disabled by default, and they will want to be enabled with the HEALTH_PORT env var (or -healthPort cli argument).
This port includes a /readyz and a /healthz which I believe are designed for kubernetes