Helix: Improvement: Add links of facts in excel (when exporting facts)

[matemies]

It would be useful to have the link to the facts when we download the datasets from the facts. That could speed up the process of QA and analysis.

https://helix.idmcdb.org/facts
Current fields:

id | gsn | serial_no | class | name |iso3 | country | displacement_type | type | document_id | parent_id | qualifier | figure | term | date | stock_date | start_date | end_date | parent_role | groups | created_by | event_id | year | event_name | event_role | sources | status | centroid | idu | excerpt_for_idu