Add custom error page (404) for WAR/SpringBoot/Quarkus

[grgrzybek]

See: #3405 (comment)

#3405 removes custom error page (404 → index.html) from web.xml. This was a tricky way to handle client-side route URLs by returning index.html when user refreshes browser with URL like http://localhost:8080/hawtio/jmx.

The problems are:

• it's for WAR only
• it gives us index.html with HTTP 404 error code
• it's also returning index.html for static resources like http://localhost:8080/hawtio/img/non-existing.png

#3405 adds new ClientRouterRedirectFilter which handles this better, but indeed it'd be nice to have proper, consistent error page handling.

[grgrzybek]

Also we should probably handle ALL errors/exception, so server-specific page is not returned.