Dispute Coordinator: Batch queries (#3459)

* disputes: Allow batch queries in dispute-coordinator

This commit moves to batch queries when responding to QueryCandidateVotes
messages. This simplifies the code in the provisioner and dispute-coordinator
by no longer requiring to make use of a FuturesOrdered when awaiting multiple
quries. Instead, the provisioner need only request the batch itself.

* node/approval-voting: Address Feedback to fail on query element missing.

* Address feedback

* Fix implementer's guide

polkadot/node/network/dispute-distribution/src/lib.rs

@@ -14,7 +14,6 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-
 //! # Sending and receiving of `DisputeRequest`s.
 //!
 //! This subsystem essentially consists of two parts:
@@ -136,7 +135,7 @@ where
 	}
 }
 
-impl<AD> DisputeDistributionSubsystem<AD> 
+impl<AD> DisputeDistributionSubsystem<AD>
 where
 	AD: AuthorityDiscovery + Clone,
 {