refactor: move from io/ioutil to io and os package (#10341)

## Description

The `io/ioutil` package has been deprecated in Go 1.16 (See https://golang.org/doc/go1.16#ioutil). Since cosmos-sdk has upgraded to Go 1.17 (#9987), this PR replaces the existing `io/ioutil` functions with their new definitions in `io` and `os` packages.

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [x] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [x] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

client/config/config_test.go

@@ -3,7 +3,7 @@ package config_test
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"testing"
 
@@ -58,7 +58,7 @@ func TestConfigCmd(t *testing.T) {
 	cmd.SetOut(b)
 	cmd.SetArgs([]string{"node"})
 	cmd.Execute()
-	out, err := ioutil.ReadAll(b)
+	out, err := io.ReadAll(b)
 	require.NoError(t, err)
 	require.Equal(t, string(out), testNode1+"\n")
 }

client/config/toml.go

@@ -2,7 +2,6 @@ package config
 
 import (
 	"bytes"
-	"io/ioutil"
 	"os"
 	"text/template"
 
@@ -43,7 +42,7 @@ func writeConfigToFile(configFilePath string, config *ClientConfig) error {
 		return err
 	}
 
-	return ioutil.WriteFile(configFilePath, buffer.Bytes(), 0600)
+	return os.WriteFile(configFilePath, buffer.Bytes(), 0600)
 }
 
 // ensureConfigPath creates a directory configPath if it does not exist

client/keys/add_ledger_test.go

@@ -6,7 +6,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -188,7 +188,7 @@ func Test_runAddCmdLedgerDryRun(t *testing.T) {
 				_, err = kb.Key("testkey")
 				require.NoError(t, err)
 
-				out, err := ioutil.ReadAll(b)
+				out, err := io.ReadAll(b)
 				require.NoError(t, err)
 				require.Contains(t, string(out), "name: testkey")
 			} else {

client/keys/add_test.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -18,7 +18,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/simapp"
 	"github.com/cosmos/cosmos-sdk/testutil"
 	sdk "github.com/cosmos/cosmos-sdk/types"
-	bip39 "github.com/cosmos/go-bip39"
+	"github.com/cosmos/go-bip39"
 )
 
 func Test_runAddCmdBasic(t *testing.T) {
@@ -220,7 +220,7 @@ func Test_runAddCmdDryRun(t *testing.T) {
 				_, err := kb.Key("testkey")
 				require.NoError(t, err)
 
-				out, err := ioutil.ReadAll(b)
+				out, err := io.ReadAll(b)
 				require.NoError(t, err)
 				require.Contains(t, string(out), "name: testkey")
 			} else {

client/keys/import.go

@@ -2,7 +2,7 @@ package keys
 
 import (
 	"bufio"
-	"io/ioutil"
+	"os"
 
 	"github.com/spf13/cobra"
 
@@ -24,7 +24,7 @@ func ImportKeyCommand() *cobra.Command {
 			}
 			buf := bufio.NewReader(clientCtx.Input)
 
-			bz, err := ioutil.ReadFile(args[1])
+			bz, err := os.ReadFile(args[1])
 			if err != nil {
 				return err
 			}

client/keys/import_test.go

@@ -3,7 +3,6 @@ package keys
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -98,7 +97,7 @@ HbP+c6JmeJy9JXe2rbbF1QtCX1gLqGcDQPBXiCtFvP7/8wTZtVOPj8vREzhZ9ElO
 
 			keyfile := filepath.Join(kbHome, "key.asc")
 
-			require.NoError(t, ioutil.WriteFile(keyfile, []byte(armoredKey), 0644))
+			require.NoError(t, os.WriteFile(keyfile, []byte(armoredKey), 0644))
 
 			defer func() {
 				_ = os.RemoveAll(kbHome)