[feature] create /health endpoint

[Woitekku]

It would be good to have a healthcheck endpoint like /health that will return 200 if proxy is up and running.
Very useful for kubernetes envs.

For now I'm doing / and accept 301 as "healthy" but it's not fully correct/ valid.

[monwolf]

Yeah, it would be fine. It would also be fine to expose some kind of basic metric for monitoring the usage.