Signatures should consume gas inside `Verify` func of ISM

[cmwaters]

Currently the gas consumed by a Verify call is fixed:

hyperlane-cosmos/x/core/keeper/keeper.go

Line 117 in f2bd6ed

sdk.UnwrapSDKContext(ctx).GasMeter().ConsumeGas(10000, "ism verification")

The ISM itself should be responsible for consuming gas. Since both message and merkle root ISMs use signatures, there's already a parameter available for consuming gas per signature

https://github.com/celestiaorg/cosmos-sdk/blob/d44ddbb106ad0cd510c170e7d23ee8a48d003ba5/x/auth/types/auth.pb.go#L176

[mbreithecker]

Hey, thanks for the hint.

Made a PR to consume gas for the signature: #154

Regarding the parameter, this requires dragging the authKeeper and params down the the actual verify method. (Having passing a consume gas method, etc.) I don't think having these many code changes is worth it.
I used the default value of 1000.

Let me know what you think.