[AHM] Poke deposits: Multisig pallet (#7700)

# Description

* This PR adds a new extrinsic `poke_deposit` to `pallet-multisig`. This
extrinsic will be used to re-adjust the deposits made in the pallet to
create a multisig operation after AHM.
* Part of #5591 

## Review Notes

* Added a new extrinsic `poke_deposit` in `pallet-multisig`.
* Added a new event `DepositPoked` to be emitted upon a successful call
of the extrinsic.
* Although the immediate use of the extrinsic will be to give back some
of the deposit after the AH-migration, the extrinsic is written such
that it can work if the deposit decreases or increases (both).
* The call to the extrinsic would be `free` if an actual adjustment is
made to the deposit and `paid` otherwise.
* Added tests to test all scenarios.

## TO-DOs
* [x] Add Benchmark
* [x] Run CI cmd bot to benchmark

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Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Giuseppe Re <giuseppe.re@parity.io>