Provide HTTP status for external probe tools

[themightychris]

Many external health probe tools, like Kubernetes' HTTP probes, need to be able to simply check whether the HTTP response status is 2xx or 3xx to know if the system is healthy. The current response body for the JSON endpoint is too complex for many systems to read, an external tool would have to parse and loop through the json to make a healthy/unhealthy determination

Similar to the --fail-command-on-failing-check option for the CLI check, an optional query param for the JSON check to make it return a 503 status instead of a 200 status if any checks are failing would be very helpful

[freekmurze]

Feel free to send a PR to add this to the package. Make sure to include tests and update docs.

[francoisauclair911]

@themightychris are you working on this ? We can team up if you want
#90