[FEATURE] Switch backend container to Graviton

[zganger]

Graviton performs better and consumes less power and therefore costs 20% less than intel systems. We can adopt it for our backend containers.

Steps:

• add --platform=linux/arm64 to docker builds in GitHub actions
  • https://github.com/kciter/aws-ecr-action - using the extra_build_args option
• update the ECR task role to use graviton/ linux ARM hosts to run the jobs
• merge and deploy

[zganger]

note: we could consider on Frontend containers as well but I haven't tested. That could be a separate issue if we like this.

[mikeyavorsky]

Doesn't work without arm64 Github Actions runner (currently in private beta?)