feat(statement-distribution): handle `ActiveLeavesUpdateSignal`

## Issue summary

We should:

- Update the current handler, the new handler should only query the `prospective_parachains_mode`, we should not check if `ProspectiveParachainsMode` is `Disabled`

- (`handle_active_leaves_update`) https://github.com/paritytech/polkadot-sdk/blob/fa52407856c11ee138a32f2ba744f774fac984d5/polkadot/node/network/statement-distribution/src/v2/mod.rs#L549

- (`handle_deactivate_leaves`) https://github.com/paritytech/polkadot-sdk/blob/fa52407856c11ee138a32f2ba744f774fac984d5/polkadot/node/network/statement-distribution/src/v2/mod.rs#L787

- (`send_pending_cluster_statements`) https://github.com/paritytech/polkadot-sdk/blob/73a0bca9cbcadb6798b72a5ebc18cf714b3fca25/polkadot/node/network/statement-distribution/src/v2/mod.rs#L940

### Acceptance Criteria

- [ ] Implement Polkadot-SDK tests
- [ ] Includes https://github.com/paritytech/polkadot-sdk/pull/8510 fix