chore: lower the default mempool min gas price (#2843)

## Overview

The mempool minfee seems too high as the goal of it is just to reduce
spam if the blocks are empty. The proper solution will come with a
consensus critical dynamic minfee. For now the default should be lowered
by an order of magnitude.

## Checklist

- [x] New and updated code has appropriate documentation
- [x] New and updated code has new and/or updated testing
- [x] Required CI checks are passing
- [x] Visual proof for any user facing features like CLI or
documentation updates
- [ ] Linked issues closed with keywords

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Adjusted the minimum gas price settings for better transaction
filtering efficiency.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

(cherry picked from commit 1eb203c)

app/default_overrides_test.go

@@ -61,5 +61,5 @@ func TestDefaultAppConfig(t *testing.T) {
 
 	assert.Equal(t, uint64(1500), cfg.StateSync.SnapshotInterval)
 	assert.Equal(t, uint32(2), cfg.StateSync.SnapshotKeepRecent)
-	assert.Equal(t, "0.1utia", cfg.MinGasPrices)
+	assert.Equal(t, "0.002utia", cfg.MinGasPrices)
 }

pkg/appconsts/initial_consts.go

@@ -20,7 +20,7 @@ const (
 	// DefaultMinGasPrice is the default min gas price that gets set in the app.toml file.
 	// The min gas price acts as a filter. Transactions below that limit will not pass
 	// a nodes `CheckTx` and thus not be proposed by that node.
-	DefaultMinGasPrice = 0.1
+	DefaultMinGasPrice = 0.002
 
 	// DefaultUnbondingTime is the default time a validator must wait
 	// to unbond in a proof of stake system. Any validator within this