KPI download for cohorts other than 6

[mbarton]

At the moment the KPI download code is hard-coded to cohort 6, which finished on the 1st of December 24 although data submission is ongoing until January 25.

@nikyraja @SAbdin93 do you need the option to select the cohort for the download?

[nikyraja]

We will do in future: for now we only need cohort 6, from spring next year we'll need cohort 7 data. We will retain our downloads so we may not necessarily need a filter, however I fell this would be good to build instead of hard coding to another cohort?