Adding support Digital Key management

[erikbosch]

Digital Keys are becoming common for vehicles and there is even standardization ongoing within the Car Connectivity Consortium (e.g. CCC Digital Key Release 3). This is a complex area and it is likely so that VSS is not suitable to handle all aspects of digital keys as the procedures for registering keys may vary considerably and may involve aspects like token/certificate evaluation and physical steps that must be performed within a vehicle. There are however areas where VSS representation could be useful. One potential use-case is to offer the driver/owner an overview of which digital keys that have been defined for the vehicle and the status of them. VSS could potentially be used to trigger certain management steps, like adding or removing a key. Note however that VSS should not in itself be responsible for security critical functionality, like validating that request have been signed by the trusted primary key.

The purpose of this PR is to initiate a discussion on if this makes sense to add to VSS,

[ppb2020]

I am in agreement that we may need to define some signals in this area. We may not be able to define what these signals are at this time, but we can start defining where they should reside in the tree. I can certainly see signals indicating whether the user has decided to block or enable sharing digital keys.

[tspreck]

@tguild you onto this one also _ I know we were discussing the CCC activities the other day and how we could do something in the CV BoF group for fleet management & digital keys

[erikbosch]

Temporarily removed