Where in the pom.xml file and using what attribute do I set the module to being free?
You don't any more. You override the module hook method to return true instead of false. Same with Maker support.
Do I have to add a gateway hook? Right now, my module just has a common package. Does this mean I have to add a gateway package with a gateway hook with a method isFreeModule() that returns true?
Yes. I'm a bit surprised that any module would work without the hook classes.
It does do something it imports the jar files into all the scopes of Ignition. It is interesting that the build pom.xml does not use the tag true when I add it to the path build/plugins/plugin/configuration. The intellisense in the IDE seems to think that is a valid tag.
The free module marker used to be in the module.xml
file. But that was too easy for bad actors to leverage. Now the code must affirmatively signal that it is free.