Relax force_default_xcm_version for testnet system parachains (#2385)

This PR fixes two things:
- relax `force_default_xcm_version` for testnet system parachains (e.g.
BridgeHubWestend has now 2 and there is no way to change it to 3, so we
need to call `force_xcm_version(3)` for every parachain that it is
connected to, because we send XCMv3 messages)
- add `Storage` item to `PolkadotXcm` pallet definition (now we cannot
see storage items for `pallet_xcm` in PJS)


## TODO

- [ ] when merged open PR to `polkadot-fellows/runtimes` repo

cumulus/parachains/runtimes/collectives/collectives-westend/src/xcm_config.rs

@@ -178,8 +178,10 @@ impl Contains<RuntimeCall> for SafeCallFilter {
 						pallet_collator_selection::Call::add_invulnerable { .. } |
 						pallet_collator_selection::Call::remove_invulnerable { .. },
 				) | RuntimeCall::Session(pallet_session::Call::purge_keys { .. }) |
-				RuntimeCall::PolkadotXcm(pallet_xcm::Call::force_xcm_version { .. }) |
-				RuntimeCall::XcmpQueue(..) |
+				RuntimeCall::PolkadotXcm(
+					pallet_xcm::Call::force_xcm_version { .. } |
+						pallet_xcm::Call::force_default_xcm_version { .. }
+				) | RuntimeCall::XcmpQueue(..) |
 				RuntimeCall::MessageQueue(..) |
 				RuntimeCall::Alliance(
 					// `init_members` accepts unbounded vecs as arguments,