Document best practices in case of AWS ECR error "already has the maximum allowed number of images which is '1000'"

[shiroyasha]

https://docs.aws.amazon.com/AmazonECR/latest/userguide/service_limits.html

It seems that AWS ECR is limiting the number of Docker images on their side. This makes regular releases on every master build for example, more painful than expected.

We should figure out and document what are the best practices in this case. This is not Semaphore's fault, but I suspect that our users will hit this limitation sooner or later and struggle with a solution.

[ghost]

Please let me or @csidyel know when this issue is resolved so we can update the customer. Thanks!