Bridge: check bridge GRANDPA pallet call limits from signed extension (#4385)

silent, because it'll be deployed with the
https://github.com/paritytech/polkadot-sdk/pull/4102, where this code
has been introduced

I've planned originally to avoid doing that check in the runtime code,
because it **may be** checked offchain. But actually, the check is quite
cheap and we could do that onchain too.