Generate container version.json outside from the CI

[jmaupetit]

Purpose

At the time of writing, we generate container's version.json file during the CI build. We think this file should be generated every time we build the container, whatever the context is (CI, local build, etc.).

Proposal

Move the version.json file generation to the make build rule. If no CI environment variable is found, fallback to local files (using git, etc.).