Versioning generation behaviour. #80
Description
Add functionality to generate versioned traits in trait-gen.
All of the trait-view versions for a particular trait should be generated into the same file.
Json schema will need to be updated.
Acceptance Criteria
Follow the structure outlined in OpenAssetIO/OpenAssetIO-MediaCreation#90
Apart from these changes:
The unversioned default trait should be an identical copy of the v1 trait.
The unversioned default trait should have a deprecation warning. In C++ this is via the [[deprecated]] attribute on the class. In python it's on the constructor, and use the pythons warnings module.