Add Logging

[LordRekishi]

Use built-in logging tool Logback to make the app create and store logs in logfiles about the status and health of the app.
This tool is configured in either application.properties or in a file we create called logback-spring.xml.

How should the logger be configured? Which level of messages do we want to log?

[helenahalldiniths]

I think it is a good idea to put it in logback-spring.xml, as a way of achieving SoC (Separation of concern).

I think "info" is a good level, however if we need to debug the application (if something isn't working) then I think we should switch to "debug".