Hello
I have refactored docker builder image for RPM packages.
Added multiarch support

https://github.com/sergey-safarov/kamailio-builder

Resulting docker images available
https://github.com/sergey-safarov/kamailio-builder/pkgs/container/kamailio-builder

Before creating a pull request to https://github.com/kamailio/pkg-kamailio-docker I want to discuss this tool with the community.
Maybe need to change the tags naming format.
Or separate into different repos "manifest" and arch-specific images.

Sergey