Add Docker HEALTHCHECK to images

[eartharoid]

Add a new /health route that requests to aren't logged.
Fetch every 15 seconds (5s timeout), 3 retries, so if the bot is unresponsive for more than a minute, it is restarted automatically.

• https://www.howtogeek.com/devops/how-and-why-to-add-health-checks-to-your-docker-containers/
• https://docs.docker.com/engine/reference/builder/#healthcheck