Replace deprecated ioutil with io and os (#20776)

* Replace ioutil with io and os

* Replace ioutil in utils/file.go

* Minor fix to tests and excluded files

Co-authored-by: Tim Scheuermann <tim.scheuermann@mattermost.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/authorization_test.go

@@ -7,7 +7,7 @@ import (
 	"context"
 	"encoding/csv"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"strconv"
 	"strings"
@@ -133,7 +133,7 @@ func TestSessionHasPermissionToGroup(t *testing.T) {
 	require.NoError(t, e)
 	defer file.Close()
 
-	b, e := ioutil.ReadAll(file)
+	b, e := io.ReadAll(file)
 	require.NoError(t, e)
 
 	r := csv.NewReader(strings.NewReader(string(b)))