Olivero: Design 404 "Page not found" and 403 "Forbidden/Access denied" pages

Problem/Motivation

• We currently have a basic page layout for both of the 404 and 403 pages (see links below).
• 404 | https://8-x-1-x-cc0mon7tao0zanzkclnbhi5qzhkajd5b.tugboat.qa/foo
• 403 | https://8-x-1-x-cc0mon7tao0zanzkclnbhi5qzhkajd5b.tugboat.qa/admin/content
• The core function of these pages is to let the user know where to go next, however, I'd like to see us come up with a creative design that makes these pages more interesting and complements the general look and feel of this theme.

Proposed resolution

• The error page can be minimalist and funny. Users may be upset if they can’t find what they’re looking for, however, why not take this opportunity to lift their spirits, by adding some graphics that are light-hearted.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet