This PR brings the fundamentals necessary for Velocity transmission from the Server app to the OpenVR driver.

What's added:

• New config toggle, default is set to false (separate file for future expandability)
• Per tracker config flag write (for future expandability + follows existing architecture)
• Velocity calculation and write per tracker.

What's missing:

• Protobuf Messages and Bridge, meaning while we will be able to calculate velocity, it'll not be sent anywhere for consumption - this will be a separate PR (Velocity MVP. Protobuf Bridge and Messages Update for Velocity Data Exchange. #1754)
• GUI, since it's an MVP, no runtime config change, only persistent config file read on server startup.

Technicalities:
Velocity is being calculated based on the final position resolved in HumanSkeleton and its previous delta over the last tick.
Delta is going through a sanity check before being used in order to discard noisy updates and spikes.

Addresses the issue: #25