Change : consider Operational dispatch class

It would be good to change normal dispatch class for some important calls:

- pallet_transaction_pause::pause_transaction
- pallet_omnipool::set_asset_tradable_state
- pallet_stableswap::set_asset_tradable_state

it should help when we need to pause transaction, as operational class has the highest priority and ignores block weight limits.

To research: verify that operational class does not have any "side effects".