Created 'custom_denied' hook to allow customisation of permission denied notifications

[ddb4github]

Feature Request

Apply 'custom_denied' hook to permission denied branch in include/auth.php for customized login/logout/denied/timeout interface

Is your feature request related to a problem? Please describe

For graph related permission denied, custom_denied hook had beed added since #2426 for permission_denied.php page.
But for general permission denied, Cacti still show buildin permission denied message.

Describe the solution you'd like

Apply 'custom_denied' hook to permission denied branch in include/auth.php

Describe alternatives you've considered

Merge permission_denied.php and include/auth.php as one entrance.

Additional context

PR #3475 was created for this feature request.