Add Docker healthcheck

Closes #1535 (closed)

Adding a Docker healthcheck right now is quite messy. For it to be convenient for both developers and sysadmins, we need the --start-interval option, which makes healthchecks happen a lot faster when the container starts. When it becomes healthy, the healthchecks happen less often. This is still being implemented and will only be fully released in Docker 25.0.

I made the healthcheck call /api/v1/public-key/, the simplest endpoint, using wget since curl is not installed in the containers and we can do without it.

I added # syntax=docker/dockerfile:1 to the Dockerfiles so they use the most up-to-date Dockerfile syntax, which already provides this option. Docker engines that do not support this option will just ignore it, so you'll have to wait for one minute for the container to become healthy instead of just a few seconds. The Compose file for the dev architecture will override the interval to compensate for the lack of support of this option.