Adds `vested_transfer` to Vesting pallet (#5029)

* Add the vested_transfer function with tests

* Add VestingDeposit for minimum amount to create a new schedule

* Remove irrelevant file commit

* Bump spec

* Add weight comment

* Fix CI build

* Make the check before the transfer

* Update frame/vesting/src/lib.rs

Co-Authored-By: Shawn Tabrizi <[email protected]>

* Update frame/vesting/src/lib.rs

Co-Authored-By: Shawn Tabrizi <[email protected]>

* Update frame/vesting/src/lib.rs

Co-Authored-By: Bastian Köcher <[email protected]>

* Update frame/vesting/src/lib.rs

Co-Authored-By: Bastian Köcher <[email protected]>

* Update frame/vesting/src/lib.rs

Co-Authored-By: Bastian Köcher <[email protected]>

* Add tab to line 249

* Rename to `MinVestedTransfer` for clarity

Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>