Flexible PostgreSQL configuration

• Make the PostgreSQL plugin configurable for alternative docker images that use different users, paths or startup options
• Provide the database administrator password as an environment variable
Flexible MariaDB configuration

• Make the MariaDB plugin configurable for alternative docker images that use different users, paths or startup options
• Provide the database administrator password as an environment variable
Flexible MongoDB configuration

• Make the MongoDB plugin configurable for alternative docker images that use different users, paths or startup options
• Provide the database administrator password as an environment variable
Flexible Redis configuration

• Make the Redis plugin configurable for alternative docker images that use paths or startup options
DRY up the database plugins
Fix indentation