feat: double auth tx size cost per byte from 10 to 20 (#7249)

Closes: #XXX

## What is the purpose of the change

Doubles auth tx size cost per byte from 10 to 20.

CHANGELOG.md

@@ -57,6 +57,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * [#7106](https://github.com/osmosis-labs/osmosis/pull/7106) Halve the time of log2 calculation (speeds up TWAP code)
 * [#7093](https://github.com/osmosis-labs/osmosis/pull/7093),[#7100](https://github.com/osmosis-labs/osmosis/pull/7100),[#7172](https://github.com/osmosis-labs/osmosis/pull/7172) Lower CPU overheads of the Osmosis epoch.
 * [#7203](https://github.com/osmosis-labs/osmosis/pull/7203) Make a maximum number of pools of 100 billion.
+* [#7249](https://github.com/osmosis-labs/osmosis/pull/7249) Double auth tx size cost per byte from 10 to 20
 * [#7259](https://github.com/osmosis-labs/osmosis/pull/7259) Lower gas and CPU overhead of chargeTakerFee (in every swap)
 * [#7258](https://github.com/osmosis-labs/osmosis/pull/7258) Remove an iterator call in CL swaps and spot price calls.
 

app/upgrades/v22/upgrades.go

@@ -23,6 +23,14 @@ func CreateUpgradeHandler(
 			return nil, err
 		}
 
+		// Increase the tx size cost per byte to 20 to reduce the exploitability of bandwidth amplification problems.
+		accountParams := keepers.AccountKeeper.GetParams(ctx)
+		accountParams.TxSizeCostPerByte = 20 // Double from the default value of 10
+		err = keepers.AccountKeeper.SetParams(ctx, accountParams)
+		if err != nil {
+			return nil, err
+		}
+
 		return migrations, nil
 	}
 }