Context:

Add a public API to use the existing export report definition functionality. We can reuse the accessToken added for json export of report results. 

Endpoint Details:
POST /public/export/report/definition/json
Takes json array of report IDs, returns json array of report definitions
Uses same accessToken as json export of report results

AT:

• a public API exists which takes a set of report IDs and returns report definitions
• this API requires a valid json export token (defined in config, same as for report result json export)
• Note that documentation will be added with separate docs ticket