Provide tutorial Docker Compose files for MongoDB and Postgres

Now that we have Docker Compose files for the tutorial (based on MySQL), we should prepare the path to variants of the tutorial for each connector. As a starting point, we should:

• Provide example Docker images for MongoDB and Postgres with sample data akin to the one for MySQL
• Provide Docker Compose files for these other connectors
• Adapt the tutorial so it provides links to all the Compose files for all the connectors

I think the tutorial itself can remain focused on MySQL for the time being (although it may be desirable to let readers even choose which connector they'd like to use and provide them with a dedicated tutorial version for each), as it should be enough to get started with Debezium, independently of the specific connector they'd like to use eventually.