Allow for more flexibility with custom large projects

GPT does currently allow for custom large projects but this is still a little limited. It expects the large projects to have been imported by GPT Data Generator and for it to follow the folder structure we've designed for that.

Currently it's not possible to configure GPT to point at an existing large project due to the following:

• GPT always expects the large project to be under a root and subgroup and isn't able to take just a full existing path as an override
• GPT will always perform the test data version check that wouldn't be applicable for custom projects and advanced usage. This check should be configurable.

Task is to allow GPT user to point it directly at their own existing large project for advanced use cases.