Custom error page for authorization exceptions

[tbragin]

Authorization exceptions are much less ambiguous now as a result of #4777

However, we could probably take steps to make this common error message even more friendly through a custom page that no longer shows the search spinner, buries the stack trace even more, and directs the user to contact the administrator if they believe they received this message in error.

[kobelb]

This will largely be addressed by #20277