Confusing plugin argument documentatio: `ecr` & `gcr`

The documentation for plugin arguments could be improved.
It is not clear that many plugins inherit from plugins/docker (including arguments).

For example, the ecr plugin does not state that it is build on top of plugins/docker as hinted here.

In contrast, the gcr plugin does so and makes it transparent that one should look up the arguments from plugins/docker.

This confusion costed me several hours until I realized that I can also use argument build_args_from_env (from plugins/docker) in plugins/ecr.
The ecr plugin has its own argument documentation which hints that only these might work and gives no hint that arguments from plugins/docker are also valid.

The fact that ecr has a dedicated argument build_args whereas plugins/docker has build_args_from_env makes it even more unlikely that the latter is accepted in ecr.