Chill on behalf of the pool.

The dispatch origin of this call can be signed by the pool nominator or the pool root role, same as [Pallet::nominate].

Under certain conditions, this call can be dispatched permissionlessly (i.e. by any account).

Conditions for a permissionless dispatch:

• When pool depositor has less than MinNominatorBond staked, otherwise pool members are unable to unbond.

Conditions for permissioned dispatch:

• The caller has a nominator or root role of the pool. This directly forward the call to the staking pallet, on behalf of the pool bonded account.