Use libcovebods for data checks rather than developing more here

This library already has a lot of data checks coded and tested.

While it may not be suitable for use straight away (eg some of the ways it currently works use high memory with large files and that may not be suitable here, it only supports JSON not JSON Lines) it's in the plan to tackle those issues anyway so being forced to tackle them now is only a good thing!

[radix0000]

Once we have battle tested the current basic consistency checks and have a more concrete idea of the requirements, it will probably make sense to revisit this at some point.