Add sample and documentation to Zephyr Project

[beriberikix]

Currently Zephyr hosts Device Management samples & documentation for device management projects like UpdateHub & Hawkbit. We should add Golioth there as well. It is unclear the policy around adding samples - both these projects have an open source server implementation. We need to verify with the Zephyr maintainers if it would be sufficient to include Golioth if only our client is open source.

[beriberikix]

@0Grit while this is technically documentation, it is probably a task for your team!

[beriberikix]

From David Brown on the TSC list:

"From a testing perspective, I would argue that the best scenario would be for the service to be available as a service to both Zephyr developers and to CI so that the code would be testable (currently, none of the existing ones have tests). Perhaps accounts could be provided to Zephyr developers that support a small number of devices."

He further suggested we bring this up in an upcoming TSC meeting.

[0Grit]

Good call. @golioth/firmware