GPT 2.0.0: Explore way handle different Large Projects in GPT

With #201 (closed) progressing and hopefully completed soon there's a possible further iteration around large projects we could do.

At the moment the change will "lock" us into gitlabhq, which will be fine for most users. However some will still want to test their own as well as ourselves having another test project based on linux.

Task then is to explore a good way to enable users to switch the project to linux or their own. At first I was thinking to extrapolate the large project config out from environment conf but with this change it may make more sense to keep it in environment config and go down the route of saying the same large project is expected on each storage node.