Update mariadb-server.NEWS with information about MariaDB 11.8 and extend README

Similar to what was done for MariaDB 10.11, this new long-term supported versions that users upgrading from both Debian Bookworm and Ubuntu Noble, or older, deserve to have additional information.

The upgrade from 10.11 to 11.8 does not include any Debian-specific items.

Also extend the server README to give exact commands on how to create new users and configure server to accept connections on the network from remote hosts.