[Pools] Follow up issues/improvements for Pools open gov integration

Tracker ticket of improvements that can be made and/or unresolved issues found in https://github.com/paritytech/polkadot-sdk/pull/3905.

[ ] (Priority: Medium) Provide a way to reap agent/delegator when account falls below ED (such as due to slashing).

In case of fully slashed pool, we might end up in a situation where delegator is reaped from pallet-delegated-staking but remains forever in pools. Worked on here (probably not a straightforward fix and affects TransferStake pools as well): https://github.com/paritytech/polkadot-sdk/tree/ankan/np-reap-fix
[ ] (Priority: Low): Improve Delegation staking apis. We have register but no unregister. This could be part of the above issue where we provide unregister and that is the only way pool accounts are reaped.
[x] (Priority: High) Bot and runtime apis for helping with applying pending slashes. https://github.com/paritytech/polkadot-sdk/issues/4630
[x] (Priority: High) Script for permissionlessly migrating all nominator delegations.
[ ] Fuzz (https://github.com/paritytech/polkadot-sdk/issues/424) + Remote ext tests (https://github.com/paritytech/polkadot-sdk/issues/4629) for DelegateStake adapter.
[x] Runtime apis for delegation based NP: https://github.com/paritytech/polkadot-sdk/pull/4537.

paritytech / polkadot-sdk