Shared infrastructure between GCV and GCV idea plugin aren't shared

[FinlayRJW]

What happened?

Currently both GCV and the idea plugin have to parse the gcv-maven-repositories.xml file but they have seperate implementations of the classes todo this. This means if one changes the other breaks

What did you want to happen?

The code for parsing the XML should be stored in a separate project in this repo which both reference so there is a single source of truth