Update validation reporting to work without LaTeX

[carlhiggs]

To minimise dependencies and reduce overall Docker image size, the latest edits have been trialling removing LaTeX from the environment. But this means that the validation reporting won't work --- so that will need to be updated. A good option will be to update it to use the within-python pdf generation approach taken for the scorecard reports. This is a bit more flexible / easy to run any.

But for now -- this is a note that we need to update the validation reporting code to support automated report generation.