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 <[email protected]>