Added support for arm64

[devantler]

closes #158, closes #113 I tested that this worked on my home cluster.

I used the Jetty image behind a reverse proxy and built my .puml files with VScode pointing to the server.

Could you please add official support, as this is an easy fix?

EDIT: Untill then this image works for arm64: devantler/plantuml-server:jetty

[devantler]

If this has interest a bake-definition could also be added, so you can easily manage supported architectures. See https://github.com/docker/metadata-action#bake-definition

[stevehipwell]

@arnaudroques do you have an idea when you're going to be releasing the next PlantUML version so this action will run?