Is your feature request related to a problem?

It seems to be published only amd64 image. I want to run docker-mailserver in arm64 environment like raspberrypi4.

Describe the solution you'd like

Add multi-architecture image build workflow.
I think we can use docker buildx.

Alternatives you've considered

Who will that feature be useful to?

Those who want to install docker-mailserver in various architectures.

What have you done already?

What are you going to contribute?

Additional context