Maintain container image for arm64 architecture

[MartinAhrer]

No container image exists for arm64 architecture

I'm running a container based build pipeline on arm64 nodes. As no levant image exists for this architecture I'm currently maintaining a very simple custom image based on arm64v8/alpine:3. A levant binary already exists for the arm architecture.

Would be helpful to have one built in sync with the amd64 image pushed to Docker hub.

[MartinAhrer]

This is probably a duplicate of issue #421