message: root: Update CHANGELOG for Launchpad exports
diff: ### Added
  +- @cosmjs/launchpad: Export distribution module msg types
  + `MsgFundCommunityPool`, `MsgSetWithdrawAddress`, `MsgWithdrawDelegatorReward`,
  + `MsgWithdrawValidatorCommission` and type checker helper functions.
  - @cosmjs/utils: Added `assertDefinedAndNotNull`.
  ### Changed
  