Install dbconfig-no-thanks package

[20th]

Description

The opendmarc package in Debian Buster includes an SQL schema to automatically create a MySQL database on installation. To do this, it has a dependency on dbconfig-mysql package which is installed during the build. However, since docker-mailserver does not actually have a MySQL server running, this results in the following errors during the build process:

Setting up opendmarc (1.3.2-6+deb10u2) ...
dbconfig-common: writing config to /etc/dbconfig-common/opendmarc.conf

Creating config file /etc/dbconfig-common/opendmarc.conf with new version
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2).
unable to connect to mysql server.
error encountered creating user:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
dbconfig-common: opendmarc configure: noninteractive fail.
dbconfig-common: opendmarc configure: ignoring errors from here forwards
populating database via sql...  done.
dbconfig-common: flushing administrative password
invoke-rc.d: could not determine current runlevel
invoke-rc.d: policy-rc.d denied execution of start.

It is not critical because the errors are ignored, but they can be fixed completely by explicitly installing the alternative dbconfig-no-thanks package.

As far as I can tell, opendmarc is not configured to use the database in anyway, so this change does not remove any functionality. But this way, since dbconfig-mysql does not pull its dependencies (mariadb-client-10.3, mariadb-client-core-10.3, mariadb-common, mysql-common), the resulting image is a little bit smaller:

623MB with dbconfig-mysql
571MB with dbconfig-no-thanks

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[georglauterbach]

50MB Image size reduction? Nice!

Thank you for submitting this PR, very welcome!

[wernerfred]

Thanks for your contribution!