Add Oracle Express

[krlmlr]

https://container-registry.oracle.com/ords/f?p=113:4:113527252984960:::4:P4_REPOSITORY,AI_REPOSITORY,AI_REPOSITORY_NAME,P4_REPOSITORY_NAME,P4_EULA_ID,P4_BUSINESS_AREA_ID:803,803,Oracle%20Database%20Express%20Edition,Oracle%20Database%20Express%20Edition,1,0&cs=3OpgTeXIrAh21MiQYaLW6Wf5upICTa6gb9XYDlMFvTTVsO45eMLsWa3Y2RAcW-gF6CrK-7QnYZNP1wkeBxc3iDA

Oracle Free is version 23, Oracle Express is version 21. We want to test against an older version of Oracle too.

Substituting container-registry.oracle.com/database/free:latest with container-registry.oracle.com/database/express:latest did not work out of the box for me, more work is needed. This should live in a separate Docker Compose file, and expose the connection under a different port (1520? 1522?).

[aavanesy]

Two commits are missing here because of a typo.