This provides the TFF orchestration logic connecting the common server logic
which applies aggregated model deltas to the server model with a
ClientDeltaFn that specifies how weight_deltas are computed on device.
A tff.templates.MeasuredProcess that broadcasts the
model weights on the server to the clients. It must support the signature
(input_values@SERVER -> output_values@CLIENT). If set to default None,
the server model is broadcast to the clients using the default