Support public ECR for ECRPushImage task

The documentation notes "The image tag will be of the form aws_account_id.dkr.ecr.region.amazonaws.com/imagename" however, a public ecr has the format of `public.ecr.aws//`

Is there a way to specify a public ECR or should this be a feature request?

Start by reviewing the ECRPushImage task and the documentation describing its current image-tag format. Determine how public ECR repository and image references should be specified, then verify the expected behavior with the task's existing tests or validation flow. Done means public.ecr.aws references are supported and the documentation accurately describes the configuration.

Written by the indexing model from the issue text.