Add `healthcheck.sh` to each container

[ssoriche]

The PostgreSQL container introduced a healthcheck.sh script that is used to determine if the container is running correctly. (this leads into Kubernetes being able to tell if a container is healthy and needs to be restarted).

The other containers need appropriate scripts to ensure they are running as well.

[ssoriche]

Work has already begun on adding healthchecks, creating a todo list to help keep track

• [x] mongo
• [x] postgres
• [ ] api
• [ ] web
• [ ] github-meets-cpan