CI: use Docker Credential Helper to pull from private AWS ECR
Follow-up of !5253 (merged)
CI fix
Fixing authentication issue when using private AWS ECR to pull opam-repository
Docker images on docker build
Example master
pipeline in error: https://gitlab.com/tezos/tezos/-/pipelines/536712702
Testing
Label ci--docker
is added to run jobs building Docker images
Edited by David Dumas