feemarket: global MinGasPrice parameter (#1104)

* Add min_gas_price to feemarket params

* Add MinGasPriceDecorators

* feemarket integration tests for MinGasPrice

* Restructure integration tests

* Simplify integration tests context

We use DeliverTx context to set up the app, otherwise not all settings are initialized.
We test CheckTx with `s.app.BaseApp.CheckTx(req)`, which uses the `CheckTx` mode and context.

* Update MinGasPrice spec in feemarket module

* reorder ethermint module order for initializing genesis

* feemarket migrations for adding MinGasPrice param

* update changelog

* Additional unit tests for MinGasPrice = 0, tx gas price > 0 (PR review)

https://github.com/tharsis/ethermint/pull/1104#discussion_r884991661

* Use 0 MinGasPrice for transaction simulations

* Fix duplicate registration of feemarket GenesisState and Params (PR review)

https://github.com/tharsis/ethermint/pull/1104#issuecomment-1141893712

x/feemarket/module.go

@@ -44,7 +44,7 @@ func (AppModuleBasic) RegisterLegacyAminoCodec(_ *codec.LegacyAmino) {
 
 // ConsensusVersion returns the consensus state-breaking version for the module.
 func (AppModuleBasic) ConsensusVersion() uint64 {
-	return 2
+	return 3
 }
 
 // DefaultGenesis returns default genesis state as raw bytes for the fee market
@@ -122,6 +122,11 @@ func (am AppModule) RegisterServices(cfg module.Configurator) {
 	if err != nil {
 		panic(err)
 	}
+
+	err = cfg.RegisterMigration(types.ModuleName, 2, m.Migrate2to3)
+	if err != nil {
+		panic(err)
+	}
 }
 
 // Route returns the message routing key for the fee market module.