Generate storage info for pallet babe (#9760)

* Adding MaxEncodedLen for:
* NextConfigDescriptor
* AllowedSlots
* BabeEpochConfiguration

In prepation for adding storage information on pallet babe

* Adding stotage_info to pallet babe

Refactored UNDER_CONSTRUCTION_SEGMENT_LENGTH to become a runtime
parameter MaxSegmentLength

* Reinstate Slice as opposed to Vec

* Refactoring code to make it neater

* Replace `MaxSegmentLength` by
`UNDER_CONSTRUCTION_SEGMENT_LENGTH`
Stop exposing the bounds to the runtime

* Removing extra line

Co-authored-by: thiolliere <gui.thiolliere@gmail.com>

substrate/frame/babe/src/tests.rs

@@ -92,7 +92,7 @@ fn first_block_epoch_zero_start() {
 
 		let consensus_log = sp_consensus_babe::ConsensusLog::NextEpochData(
 			sp_consensus_babe::digests::NextEpochDescriptor {
-				authorities: Babe::authorities(),
+				authorities: Babe::authorities().to_vec(),
 				randomness: Babe::randomness(),
 			},
 		);