Check disclosivity of rates data file in prep for download utility in TPMA Explorer

[DCEW]

Given the discussion in this issue, we need to check that the rates.parquet is not disclosive, and if it is, to decide on actions to make it shareable.

[matt-dray]

Relevant to https://github.com/The-Strategy-Unit/nhp_planning/issues/454 (open the data) and https://github.com/The-Strategy-Unit/nhp_planning/issues/476 (make it shareable via API).