Add setting to fix runserver_plus debugger on custom host names

[browniebroke]

Add RUNSERVERPLUS_TRUSTED_HOSTS setting to work with Werkzeug 3.0.3+ debugger.

Werkzeug version 3.0.3 introduced a fix for a security vulnerability:

Only allow localhost, .localhost, 127.0.0.1, or the specified hostname when running the dev server, to make debugger requests. Additional hosts can be added by using the debugger middleware directly. The debugger UI makes requests using the full URL rather than only the path. GHSA-2g68-c3qc-8985

I'm running runserver_plus with Werkzeug 3.0.3 on a machine with a custom dev host (e.g. dev.mydomain.com) which means that the Werkzeug debugger no longer works.

As far as I could tell, there was no way to tell Werkzeug to trust my dev host, so adding this option to do so.

Questions

1. Should this default to settings.ALLOWED_HOSTS? It might be a good enough default on a Django project...
2. Updated the docs, let me know if I missed anything?