Split awscli image into two images

This MR splits the cloud-deploy image into two images: the cloud-deploy/aws-base (which only has the awscli) and cloud-deploy/aws-ecs (which has the update_task_definition script in it).

We're also keeping cloud-deploy image but we're starting a deprecation process with it: whenever a cloud-deploy container runs, it'll show a warning message similar to this one to let users know that they have a limited amount of time to switch to either aws-base or aws-ecs. In addition to this message, a similar note should be included in the 12.10 blog post.

Relates to gitlab#210543 (closed)