update_roles: TxDescriptor<{
    new_bouncer: NominationPoolsConfigOp;
    new_nominator: NominationPoolsConfigOp;
    new_root: NominationPoolsConfigOp;
    pool_id: number;
}>

Update the roles of the pool.

The root is the only entity that can change any of the roles, including itself, excluding the depositor, who can never change.

It emits an event, notifying UIs of the role change. This event is quite relevant to most pool members and they should be informed of changes to pool roles.