XDOCKER-284: Upgrade stable version to 15.6

15.5/mariadb-tomcat/.env

15.5/mariadb-tomcat/Dockerfile

15.5/mariadb-tomcat/docker-compose.yml

15.5/mariadb-tomcat/mariadb/init.sql

15.5/mariadb-tomcat/mariadb/xwiki.cnf

15.5/mariadb-tomcat/tomcat/setenv.sh

15.5/mariadb-tomcat/xwiki/docker-entrypoint.sh

15.5/mariadb-tomcat/xwiki/hibernate.cfg.xml

15.5/mysql-tomcat/.env

15.5/mysql-tomcat/Dockerfile

15.5/mysql-tomcat/docker-compose.yml

15.5/mysql-tomcat/mysql/init.sql

15.5/mysql-tomcat/mysql/xwiki.cnf

15.5/mysql-tomcat/tomcat/setenv.sh

15.5/mysql-tomcat/xwiki/docker-entrypoint.sh

15.5/mysql-tomcat/xwiki/hibernate.cfg.xml

15.5/postgres-tomcat/.env

15.5/postgres-tomcat/Dockerfile

15.5/postgres-tomcat/docker-compose.yml

15.5/postgres-tomcat/tomcat/setenv.sh