Use a common arg for the pipeline image

[jpverde]

The issue

Right now the pipeline module writes the pipeline file using the current release as the container image https://github.com/fluidattacks/makes/blob/main/src/evaluator/modules/pipelines/default.nix#L98

Possible solution

Make the pipeline module to be able to receive an arg with the sha256 for the makes' container image to use it as the common value for every job.