Move WIP schemas under `src/schemas` on `dev` and `vX.Y-dev` branches

[frankkilcommins]

In order to shield users from these files, the same way we do with /src, they should be present on the dev branch

• [ ] remove schemas folder - the work-in-progress schemas are in the src/schemas/validation folder
• [ ] only test the work-in-progress schema sources
• [ ] only measure test coverage for work-in-progress schema sources
• [ ] create deployable schema files from schema sources in the src/schemas/validation
• [ ] template workflow for schema publishing from vX.Y-dev branches