NGINX Plus: Server Zone Metrics are not Emitted

[mpstefan]

NGF currently does not emit any server_zone metrics from NGINX Plus. This appears to be an oversight in our exposure of metrics, so this is something we need to fix.

Reported by Dan Edgar:

Acceptance

• All server_zone metrics emitted by NGINX Plus when used as our data plane should be exposed on our metrics endpoint.
• An NGINX directive is added to every location in every server block that NGF generates so that a server_zone metric is emitted for each location.

[lucacome]

https://nginx.org/en/docs/http/ngx_http_api_module.html#status_zone