Add missing endpoints

[jpinsonneau]

This PR add the following missing endpoints:
GET /ready
GET /metrics
GET /config
GET /services
GET /loki/api/v1/status/buildinfo

These are useful when a client need status / context of running loki

[matej-g]

I'm not that knowledgeable about Loki to know whether this is a valid use case (so I'd defer to @periklis for final word), but it does not seem right to me to expose internal Loki information to tenants. They should not care about configuration etc., these information might be useful for Observatorium admins, but they are able to see these paths directly in Loki.

[periklis]

I suggest not to expose internal endpoints of Loki through the API. Literally this exposes only endpoints against the loki query-frontend. If you need such info you should use the Loki Query Frontend HTTP service.

[jpinsonneau]

Following today's discussion we are going to directly call query frontend for these endpoints

FYI this is exposed to the user as troubleshoot helper in netobserv/network-observability-console-plugin#171

Thanks for the feedback