Update HumanEval and MBPP notebooks

[olliestanley]

This updates HumanEval and MBPP instruction dataset generation notebooks to correct the output format and push their results to HuggingFace Hub, while also moving them to the new data directory.

It also changes the name of the grade-school-math-instructions directory to grade_school_math_instructions for consistency with other directories in data/datasets.

[Vechtomov]

Later we can combine all these datasets in one and add SOURCE column. Also we can increase diversity of prompts.

[olliestanley]

Later we can combine all these datasets in one and add SOURCE column. Also we can increase diversity of prompts.

I will at least combine the two code gen datasets together and test gen datasets together for now, I can do it quickly. Prompt diversity may be a bit of a challenge given the nature of the instructions but I agree we can probably introduce some at least.

[olliestanley]

Now updated to just produce 2 datasets (code gen and test gen) rather than 4.