Resolve "Continuous integration of FusionIAM docker images"

Closes #52 (closed)

Alright, after some twists and turns, here what we got in 4 stages :

• A linter stage, i'm using hadolint here. It could be improved I guess
• A build stage for the fusioniam-rockylinux8 image which will be used as base by the others
• A build stage for all the other images
• A push stage for all images and their tags, this step will only be executed for the default branch, but can also be executed manually on other branches. It will push a :latest tag, and a :branch_name-CI_COMMIT_SHORT_SHA tag.