Switch to KUKSA.val databroker

Since upstream has indicated that the C++ version of the KUKSA.val server is being deprecated in favor of the Rust implementation (known as the KUKSA.val databroker), we ideally need to switch over to stay with what is supported.  The effort will include:

• Getting the databroker to build, which requires resolving it needing newer Rust and Cargo than are present in Yocto kirkstone.
• Converting our clients to using the databroker's gRPC interface.  This had been planned against the C++ server, but is required with the databroker, as it does not implement the VISS WebSocket interface at all.  Having both servers in images for an interim period where clients are converted is likely possible, but may prove not worthwhile as the effort to make a feeder configuration to drive both of them in sync would be extra (and throwaway) work.