mariadb container create multiple database.

mariadb/docker-entrypoint-initdb.d/.gitignore

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+*.sql

mariadb/docker-entrypoint-initdb.d/createdb.sql.example

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+###
+### Copy createdb.sql.example to createdb.sql
+### then uncomment and set database name to create you need databases
+###
+
+#CREATE DATABASE IF NOT EXISTS `dev_db_1` ;
+#CREATE DATABASE IF NOT EXISTS `dev_db_2` ;
+#CREATE DATABASE IF NOT EXISTS `dev_db_3` ;