fix: override proposer rewards to 0% (#2717)

Closes #2716

## Testing

```bash
./scripts/single-node.sh
cat ~/.celestia-app/config/genesis.json
```

### Before

```genesis.json
    "distribution": {
      "params": {
        "community_tax": "0.020000000000000000",
        "base_proposer_reward": "0.010000000000000000",
        "bonus_proposer_reward": "0.040000000000000000",
        "withdraw_addr_enabled": true
      },
```

### After

```genesis.json
    "distribution": {
      "params": {
        "community_tax": "0.020000000000000000",
        "base_proposer_reward": "0.000000000000000000",
        "bonus_proposer_reward": "0.000000000000000000",
        "withdraw_addr_enabled": true
      },
```

(cherry picked from commit dfd9959)

app/app.go

@@ -143,7 +143,7 @@ var (
 		capability.AppModuleBasic{},
 		stakingModule{},
 		mintModule{},
-		distr.AppModuleBasic{},
+		distributionModule{},
 		newGovModule(),
 		params.AppModuleBasic{},
 		crisisModule{},

app/default_overrides.go

@@ -15,7 +15,9 @@ import (
 	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
 	"github.com/cosmos/cosmos-sdk/x/crisis"
 	crisistypes "github.com/cosmos/cosmos-sdk/x/crisis/types"
+	distribution "github.com/cosmos/cosmos-sdk/x/distribution"
 	distrclient "github.com/cosmos/cosmos-sdk/x/distribution/client"
+	distributiontypes "github.com/cosmos/cosmos-sdk/x/distribution/types"
 	"github.com/cosmos/cosmos-sdk/x/gov"
 	govclient "github.com/cosmos/cosmos-sdk/x/gov/client"
 	govtypes "github.com/cosmos/cosmos-sdk/x/gov/types/v1"
@@ -117,6 +119,20 @@ func (crisisModule) DefaultGenesis(cdc codec.JSONCodec) json.RawMessage {
 	})
 }
 
+type distributionModule struct {
+	distribution.AppModuleBasic
+}
+
+// DefaultGenesis returns custom x/distribution module genesis state.
+func (distributionModule) DefaultGenesis(cdc codec.JSONCodec) json.RawMessage {
+	params := distributiontypes.DefaultParams()
+	params.BaseProposerReward = sdk.ZeroDec()  // 0%
+	params.BonusProposerReward = sdk.ZeroDec() // 0%
+	return cdc.MustMarshalJSON(&distributiontypes.GenesisState{
+		Params: params,
+	})
+}
+
 type ibcModule struct {
 	ibc.AppModuleBasic
 }

app/default_overrides_test.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/celestiaorg/celestia-app/app/encoding"
 	"github.com/cosmos/cosmos-sdk/types"
+	distributiontypes "github.com/cosmos/cosmos-sdk/x/distribution/types"
 	govtypes "github.com/cosmos/cosmos-sdk/x/gov/types/v1"
 	"github.com/stretchr/testify/assert"
 )
@@ -32,3 +33,21 @@ func Test_newGovModule(t *testing.T) {
 	assert.Equal(t, oneWeek, *govGenesisState.DepositParams.MaxDepositPeriod)
 	assert.Equal(t, oneWeek, *govGenesisState.VotingParams.VotingPeriod)
 }
+
+// TestDefaultGenesis verifies that the distribution module's genesis state has
+// defaults overridden.
+func TestDefaultGenesis(t *testing.T) {
+	encCfg := encoding.MakeConfig(ModuleEncodingRegisters...)
+	dm := distributionModule{}
+	raw := dm.DefaultGenesis(encCfg.Codec)
+	distributionGenesisState := distributiontypes.GenesisState{}
+	encCfg.Codec.MustUnmarshalJSON(raw, &distributionGenesisState)
+
+	// Verify that BaseProposerReward and BonusProposerReward were overridden to 0%.
+	assert.Equal(t, types.ZeroDec(), distributionGenesisState.Params.BaseProposerReward)
+	assert.Equal(t, types.ZeroDec(), distributionGenesisState.Params.BonusProposerReward)
+
+	// Verify that other params weren't overridden.
+	assert.Equal(t, distributiontypes.DefaultParams().WithdrawAddrEnabled, distributionGenesisState.Params.WithdrawAddrEnabled)
+	assert.Equal(t, distributiontypes.DefaultParams().CommunityTax, distributionGenesisState.Params.CommunityTax)
+}