Docker fields should be renamed container instead

[janderssonse]

While docker as a company was the first to broadly introduce the usage of containerfiles, the world has moved on and standardized so we are now talking containers instead of dockerimages, and there are multiple implementations supporting the standards, like docker, podman and kubernetes containers. We say Containerfile and not Dockerfile, etc any more. A few fields are still named docker... like dockers:, docker_manifests:, docker_signs: when they should really be called containers, container_manifests_ container_signs etc. So the suggestion is to support these general names, and deprecate the docker: ones, making it clearer that this is not docker-specific but for containers in general.

[caarlos0]

we have a new dockers_v2 going on, so we might instead rename it to containers whilst we remove the deprecated dockers and docker_manifests. docker_signs could be renamed to container_signs as well.

that being said, internally, dockers_v2 still uses the docker binary by default. It doesn't support other implementations (like podman) yet