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].

This directly forwards the call to an implementation of StakingInterface (e.g., pallet-staking) through [Config::StakeAdapter], on behalf of the bonded pool.

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 is the pool's nominator or root.