feat(app): Make post price txs gasless

[matthiasmatt]

No description provided.

[NibiruHeisenberg]

Instead of creating our own custom DeductFeeDecorator, what if we over-write the t.AuthInfo.Fee.Amount inside of GaslessDecorator so that the default DeductFeeDecorator takes zero coins away from the oracle?

[matthiasmatt]

Because of that behavior in the fee.go ante:

	// Ensure that the provided fees meet a minimum threshold for the validator,
	// if this is a CheckTx. This is only for local mempool purposes, and thus
	// is only ran on check tx.
	if ctx.IsCheckTx() && !simulate {
		minGasPrices := ctx.MinGasPrices()
		if !minGasPrices.IsZero() {
			requiredFees := make(sdk.Coins, len(minGasPrices))

			// Determine the required fees by multiplying each required minimum gas
			// price by the gas limit, where fee = ceil(minGasPrice * gasLimit).
			glDec := sdk.NewDec(int64(gas))
			for i, gp := range minGasPrices {
				fee := gp.Amount.Mul(glDec)
				requiredFees[i] = sdk.NewCoin(gp.Denom, fee.Ceil().RoundInt())
			}

			if !feeCoins.IsAnyGTE(requiredFees) {
				return ctx, sdkerrors.Wrapf(sdkerrors.ErrInsufficientFee, "insufficient fees; got: %s required: %s", feeCoins, requiredFees)
			}
		}
	}

if you provide 0 coins for required fees, it will fail with: insufficient fees; got: 0 required: 0