Clean up workflows around image building and ECR auth

[ejfine]

Code improvement description

right now some actions related to ECR are only in grandchild templates, but building image workflow is technicaly present in child templates but calls out to those actions. probably the build-image workflow just shouldn't be available in the child templates (only the grandchild templates)

see discussion LabAutomationAndScreening/copier-nuxt-python-intranet-app#128 (comment)