Improve CI process

[matiasgarciaisaia]

There are some issues with the new Github Actions based CI process that we should tackle:

• NodeJS installation script adds 1:20 minute sleeps (to warn us it's deprecated)
• NodeJS version is out of date and unsupported 🙃
• Base Debian version is out of date and unsupported
• mapcache and mapserver images are sharing a Docker repo (should have a different repo for each image)
• Dependencies are getting downloaded on every build (we should either cache them or build an image with the base dependencies and another one on top with the app's code)
• Dockerfile-dev is exactly the same as the first few steps of the build stage for the actual image (we should reuse the build stage, or a subset of it, for development and tests)
• There's a weird loop to retry apt packages download & installation that doesn't make sense (probably due to old network issues between CircleCI and Debian repos).