Optimize pallet_migrations storage reads in on_initialize

[tmpolaczyk]

pallet_migrations reads storage ShouldPauseXcm on every block in on_initialize, even though this is only needed for one block, during (or after?) a runtime upgrade:

moonkit/pallets/migrations/src/lib.rs

Lines 169 to 180 in 9df5da6

	fn on_initialize(_: BlockNumberFor<T>) -> Weight {
	if ShouldPauseXcm::<T>::get() {
	// Suspend XCM execution
	if let Err(error) = T::XcmExecutionManager::suspend_xcm_execution() {
	<Pallet<T>>::deposit_event(Event::FailedToSuspendIdleXcmExecution { error });
	}
	// Account on_finalize write
	T::DbWeight::get().reads_writes(1, 1)
	} else {
	T::DbWeight::get().reads(1)
	}
	}

Explore an alternative approach that pauses xcm execution in some other way that doesn't require the on_initialize hook.

Same for on_finalize.

[RomarQ]

We can probably use on_runtime_upgrade from #[pallet::hooks].