IoT central investigation

[spygi]

We want to understand better IoTCentral with the goal to eventually merge #360

Acceptance criteria

• Timebox understanding of IoT Central and potentially a brownbag

[bastbu]

@Mandur and I started to take a look at the PR. Some findings that we both had:

• We could not get OTAA with IoT Central to work on our machines, we would need to add documentation how we can make this work
• We would need to find a way to not fetch the device twins of all devices when provisioning an ABP device, as this might potentially be an expensive/chatty operation
• We would still need to check if the OTAA join checks the App Key of the device when a join request is issued

Something to consider: we could go through an ADR for IoT central support and then bring in the functionality piece by piece.