Registers a device to a site

Registers a PassiveLogic device to a site and returns the auth group the device now belongs to.

The caller must prove they are allowed to add the device to the site in one of two ways:

• Provide a userJWT from a user who has access to the site. The device making the request is the one being registered.
• Provide a followerSerialNumber when a leader device is bringing a follower onto its site.

If the device is already registered, its auth group is updated instead of creating a duplicate registration.

This call must be made on the device itself over mTLS authentication.

Only call this endpoint for devices provisioned by a webserver on v9.1.1 or older, where provisioning does not register the device correctly when initiate is called. Newer devices are registered automatically and do not need this call.