security/crowdsec-firewall-bouncer: include configuration patch

The update to 0.0.28 from PR 274213 did not include a file that sets
backend mode in new installations. If the backend is not set, the
application does not start.

This version includes the missing patch file, and also sets the
$BACKEND environment variable as a fallback. The application will
substitute it at runtime if required.

PR: 274213, 274529
Fixes: 714e7fb44f516d31f08b657b2eb9a66ae1fbf9c7