Adopting the Amazon ECR plugin

[Tobias Gruetzmacher]

Hi,

I'd like to adopt the Amazon ECR plugin:

- https://plugins.jenkins.io/amazon-ecr/
- https://github.com/jenkinsci/amazon-ecr-plugin

It's a pretty simple (3 classes) but also pretty useful plugin. No
current plans to add new features, only modernizing the plugin, updating
to the modular AWS SDK plugin and getting a release out.

I will send a PR to the repository-permissions-updater later.

Regards, Tobias