Show banner in server and client startup to drive community engagement

Show banner in server and client startup to drive community engagement

Suggest to users that they can support MariaDB development by simply giving a
star on GitHub. This patch experiments with how well such a banner works, and
may later change the contents to drive some other kind of engagement.

Client output:

    Welcome to the MariaDB monitor.  Commands end with ; or \g.
    Your MariaDB connection id is 17
    Server version: 11.8.1-MariaDB-5 from Debian -- Please help get to 10k stars at https://github.com/MariaDB/Server

    Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

    Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

    MariaDB [(none)]>

Server output:
    [Note] Please help get to 10k stars at https://github.com/MariaDB/Server

Server output if built in git directory:
    [Note] Starting MariaDB 11.8.1-MariaDB-5 from Debian source revision 1a9c3debfd6b1b16af4e501d3530b866b85c38a8 server_uid eNAjF8/wvUNM09/mSmh+k3a5o5w= as process 1359

Logs will also show as server output:
    mysqld: Version: '11.8.1-MariaDB-5 from Debian'  socket: '/run/mysqld/mysqld.sock'  port: 3306  -- Please help get to 10k stars at https://github.com/MariaDB/Server

Forwarded: no

Gbp-Pq: Name startup-message.patch