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/admin.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"runtime/debug"
@@ -261,7 +260,7 @@ func (a *App) GetLatestVersion(latestVersionUrl string) (*model.GithubReleaseInf
 
 	defer res.Body.Close()
 
-	responseData, err := ioutil.ReadAll(res.Body)
+	responseData, err := io.ReadAll(res.Body)
 	if err != nil {
 		return nil, model.NewAppError("GetLatestVersion", "app.admin.latest_version_read_all.failure", nil, "", http.StatusInternalServerError)
 	}