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/command.go

@@ -7,7 +7,6 @@ import (
 	"context"
 	"errors"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/url"
 	"regexp"
@@ -521,7 +520,7 @@ func (a *App) DoCommandRequest(cmd *model.Command, p url.Values) (*model.Command
 
 	if resp.StatusCode != http.StatusOK {
 		// Ignore the error below because the resulting string will just be the empty string if bodyBytes is nil
-		bodyBytes, _ := ioutil.ReadAll(body)
+		bodyBytes, _ := io.ReadAll(body)
 
 		return cmd, nil, model.NewAppError("command", "api.command.execute_command.failed_resp.app_error", map[string]any{"Trigger": cmd.Trigger, "Status": resp.Status}, string(bodyBytes), http.StatusInternalServerError)
 	}