Modifying the fact_id key in MyNews to be a list rather than a unique key

[Oliph]

In the mynews collection, to link the fact_id with the downloaded news articles, the _id from the fact check claim (stored in maldita) is stored in fact_id key. However, it allows only one fact_id.
It should be a list that can be append to account for the case where one news article can be associated with several fact-check.
The script in api_twitter uses that approach and can be adapted to api_mynews