Create CSCP KS4 API dataset

CSCP currently reads from a data file with hundreds of columns with obscure headers. We need a tidy version to upload to the API.

The current file is 2022-2023_england_ks4_provisional.xlsx and contains data on:
- Attainment 8 (cumulative score, average score, confidence intervals)
- Progress 8
- Grade attainment (pupil count and pupil percent)
- Achieving grades 9 - 5
- Achieving grades 9 - 4

This probably wants splitting into 2 files:
- Attainment score metrics (Attainment 8 and Progress 8)
- Grade attainment