Allow using a VirtualDevice from multiple Flows

[rbino]

Right now, Virtual Devices are spawned via a DynamicSupervisor, so they're not tied to a single Flow, but they do not provide a way to add/remove interfaces, so if another Flow needs to use the same device but the Flow that started it did not have the required interfaces in the InterfaceProvider, the attempts to publish data from the second Flow will fail.

See astarte-platform/astarte-device-sdk-elixir#6, which is a prerequisite to fix this issue.