Install aws cli in CI image

What does this MR do?

Install aws cli in CI image.

Why was this MR needed?

As part of #27269 (closed) we need to have the aws cli installed so that we can run aws ecr-public get-login-password --region us-east-1 to get the log in for the ecr public repository.

Follow the official installation instructions found at https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2-linux.html.

What's the best way to test this MR?

# Old version that doesn't have AWS installed
$ docker run --rm -it registry.gitlab.com/gitlab-org/gitlab-runner/ci:1.13.8-8 aws --version
docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"aws\": executable file not found in $PATH": unknown.

# New version that has AWS installed
$ docker run --rm -it registry.gitlab.com/gitlab-org/gitlab-runner/ci:1.13.8-9 aws --version
aws-cli/2.0.30 Python/3.7.3 Linux/5.4.39-linuxkit botocore/2.0.0dev34

Size difference

With new tools installed we have around an additional 30M added to our image.

What are the relevant issue numbers?

Reference #27269 (closed)