[feature] built-in retry mechanism on push

[anapsix]

It would be awesome to have img push to retry on failure, similar to how docker CLI does it (5 times in total, with exponential back off). Alas, img does not appear to retry on push failures.
For context, AWS ECR repos have to pre-created before pushing, and I'm using an AWS Lamba to create an ECR repo when push failure event (caused by missing repo) shows up in Cloudtrail.