include pam_auth_map.so in binary packages

Currently only the pam_user_map.c source file is included in the MariaDB source, but binary builds of this PAM module are not part of our binary RPM and deb packages.

Interested users are told to compile the module themselves:

https://mariadb.com/kb/en/library/user-and-group-mapping-with-pam/#installing-the-pam_user_map-pam-module

While it is rather easy to build, this requires compilers etc installed on the target system.

Having this module being part of the MariaDB-server package, and either installed into /lib/security (or /lib64/security) right away, or into some place under /usr/share/mysql from which it can easily be copied manually would make things more convenient.