Etherpad 1.9.0 has introduced a new /health endpoint.
It makes more sense to use this dedicated health check
than /stats coming from a plugin.
The /health response follows the Health Check Response Format
for HTTP APIs specification. Meanwhile, we can use the HTTP 200 code.
Reference: https://www.ietf.org/archive/id/draft-inadarei-api-health-check-06.html