Excel export from enrolment REST endpoints [KI]

[Brian Lewis]

Implement as per description in #1090, to action the ?xl parameter on the url by returning a workbook.

[Brian Lewis]

The workbook contains a table corresponding to the REST endpoint data, a pivot table built from that table, and a pivot chart/table combination also built from the table.

The pivot table and chart are configured to give a sensible result for the particular data.

Can be actioned from javascript, or will also work if called directly from the browser location bar ; e.g.

<site>/api/warehouse/enrol/authority?byAge&xl

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For KI workplan 2021.

[Brian Lewis]

feat(warehouse): Excel exports from Enrolment REST endpoints, using ?xl option

Resolves #1103

→ <<cset 65cca48b64a5>>