Expose MySQL Configs

[storopoli]

As discussed in #6, we need to expose the configs of the MySQL database to the user in the start-os GUI.

Use the example from syncthing: https://github.com/Start9Labs/syncthing-startos/blob/724b613c5e880e7476c93afd022d249f62a4b8d0/scripts/procedures/getConfig.ts#L3-L36

Currently it is hardcoded like this:

ENV MYSQL_USER=ulabelbase
ENV MYSQL_DATABASE=labelbase
ENV MYSQL_ROOT_PASSWORD=labelbase
ENV MYSQL_PASSWORD=labelbase
ENV MYSQL_PWD=labelbase

I don't particularly like that approach, yet many Dockerfiles include hard-coded passwords. > That's why I implemented it using the Twelve-Factor App methodology, which resulted in an exports.sh file.

But hey, let's get this up and running. I'll check the Dockerfile as soon as possible.

Originally posted by @xavierfiechter in #6 (comment)