Serves an app's health report as JSON: 200 when healthy, 503 when not.
The JSON is the report's wire form (Macaw.Host.Health.to_wire/1): each
check's result worded as text here, at the edge.
get "/healthz", Macaw.Host.Health.Plug, report: {MyApp.Health, :report, []}or as a plug in an endpoint, answering only its :path (default
/healthz) and passing every other request on.