Incompatible with awscli v2

[pda]

This plugin uses aws ecr get-login which was quietly deprected in aws/aws-cli@b83b3a5 which landed in 1.17.10 on 5th Feb (less than a month ago), and completely removed in awscli v2, which is released but not in many distribution channels (package managers etc) yet.

$ aws --version
aws-cli/2.0.2 Python/3.7.3 Linux/5.5.6-arch1-1 botocore/2.0.0dev6

$ aws ecr get-login
usage: aws [options] <command> <subcommand> [<subcommand> ...] [parameters]
...
aws: error: argument operation: Invalid choice, valid choices are:
...

This plugin should instead use aws ec2 get-login-password. However unlike get-login, get-login-password doesn't give us the ECR registry URL (including AWS account ID & region) which should be passed to the docker login command. Deriving it will add some complexity.