Update `build_federated_averaging_process` and `build_federated_sgd_process` to return the full metrics suite.

After this change, users of `tff.learning.build_federated_averaging_process`
(and the FedSGD version) will receives a named tuple of three groups of metrics: broadcast, train, and aggregation.

- `train` are the same metrics that were previously returned.
- `broadcast` and `aggregation` are metrics for the broadcast and aggregatin
  process respectively. For example, an aggregation process might report
  metrics about the client updates and the aggregated update (e.g. the global
  norms).

Previously these methods only extracted the training metrics to retain
historical behavior. This change updates the methods and callsites to return
the full metrics set (including those from the broadcast and aggregation
processes).

PiperOrigin-RevId: 317888544