Build images with deps versions

[merlimat]

Motivation

Since the dependencies are getting statically linked into the binary artifacts that we release, we need to have a good/easy way to upgrade the versions of such dependencies and make sure they are consistent for all the different builds.

Modifications

1. Use a single dependencies.yaml file to declare the dependencies
2. The versions are then converted to variable inside the Dockerfiles
3. Create (and cache) the Docker images used for building in the Github actions job

[BewareMyPower]

The snappy tar file downloaded is <version>.tar.gz.