Improve packaging

[amotl]

This is a collection of backlog items for the packaging process being added through #4.

• We might think about providing more reasonable defaults for packaging/etc/owntracks-publisher.env. Adding comments to describe the configuration options would also do no harm.

• We might think about using the version string for make debian-package ... from version.h without further ado.

• Add support for more operating systems and architectures.

  • FreeBSD (in progress by @jpmens)
  • CentOS, difficult as dependencies (gpsd, mosquitto) currently not in Epel8
  • MIPS architecture support (looking at OpenWrt here).
  • Ultimately, we might support all architectures of gpsd for OpenWrt itself in order to get maximum coverage on Embedded Linux in general: aarch64, i386, mips64, mips32, mipsel, powerpc. multiarch/crossbuild could help us here.

[amotl]

Just a note.

Maybe we should switch from the balenalib Docker images to the canonical ones for Debian?

• https://hub.docker.com/r/amd64/debian
• https://hub.docker.com/r/arm32v7/debian
• https://hub.docker.com/r/arm64v8/debian

This would align well with the canonical images for CentOS.

• https://hub.docker.com/r/amd64/centos
• https://hub.docker.com/r/arm32v7/centos
• https://hub.docker.com/r/arm64v8/centos

[jpmens]

Go ahead.