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)

x/auth/client/cli/tx_multisign.go

@@ -2,7 +2,6 @@ package cli
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"strings"
 
@@ -393,14 +392,14 @@ func makeBatchMultisignCmd() func(cmd *cobra.Command, args []string) error {
 
 func unmarshalSignatureJSON(clientCtx client.Context, filename string) (sigs []signingtypes.SignatureV2, err error) {
 	var bytes []byte
-	if bytes, err = ioutil.ReadFile(filename); err != nil {
+	if bytes, err = os.ReadFile(filename); err != nil {
 		return
 	}
 	return clientCtx.TxConfig.UnmarshalSignatureJSON(bytes)
 }
 
 func readSignaturesFromFile(ctx client.Context, filename string) (sigs []signingtypes.SignatureV2, err error) {
-	bz, err := ioutil.ReadFile(filename)
+	bz, err := os.ReadFile(filename)
 	if err != nil {
 		return nil, err
 	}