Adding Flexisip stats api OpenApi specification
Add endpoint to handle BYEs. The proxy would have a hard time finding the device ID when forwarding a BYE.
To fix that, we moved the `terminated` state to the call object itself, which makes more sense anyway since a call can only be established with a single device.
Device subobjects now only store the final state of the initial invite.
Remove format restriction on Call IDs -> They can be any string, not just UUIDs.
Fix typos
