The command is needed to install/upgrade databases. It should therefore
reside in the server-core package, as that package is supposed to contain
all necessary tools to start and run the database (although manually,
there are no automation or service scripts included in server-core by
design).

Also add Breaks+Replaces in the control so upgrades will not complain about
overwriting files in previously installed packages of different name.

This was adopted from Debian where this change has been since Nov 4, 2018.
https://salsa.debian.org/mariadb-team/mariadb-10.1/-/commit/3689350ad30916aa68fe2c1b35c290fb5095bc9b

In addition, also move all *.sql files referenced mysql_install_db for
the same reasons.