Support PetScan IDs (PSIDs) as contest criteria

[jhsoby]

In relation to #33, User:Rubén Ojeda (WMES) asked if it was possible to use PetScan as a criterion for which articles should count in the contest. We currently don't have support for that, but it would be good if we did, seeing as PetScan gives its own unique ways of combining and filtering various sources of pages.

[zache-fi]

This is now possible through https://sparqlbridge.toolforge.org , ie you can do federated SPARQL query to sparqlbridge which exposes the Petscan results. Though if we are using WQS then it needs to be routed through https://qlever.wikidata.dbis.rwth-aachen.de/wikidata , but i hope that #98 will go through and Qlever would be primary endpoind.

Note: adding native Petscan support is generally a good idea and shoud be done at some point.