Support ES equivalent of `/_cluster/health` endpoint

Is your feature request related to a problem? Please describe.

I'm using 3rd party app that I don't control, require access to the /_cluster/health endpoint, which doesn't exist in zincsearch

Describe the solution you'd like

I think we can simply map this endpoint to the existing /healthz --> github.com/zincsearch/zincsearch/pkg/meta.GetHealthz (4 handlers) ?

If this sounds reasonable, I can create a PR for this.

Thanks!