Support for file uploads about wikidata-toolkit

[wetneb]

@Tpt curious what you think about this! :)

[Tpt]

It's a great question! I would say explicitly proviidng code for uploading file is out of scope of Wikibase but we definitely should provide some ways to make it easy to do action API calls not explicitly supported by WDTK using the ApiConnection object. Interop with existing Java client(s) would be even better indeed. We should also keep in mind the there is a work in progress REST API for Wikibase and we might want to migrate WDTK to it, maybe dropping the action API support in the process.

[wetneb]

Let's close this then, we will try to do upload actions on our own (accessing the credentials from Wikidata-Toolkit in some way, for instance by abusing JSON serialization)

[wetneb]

I looked into this and it seems that we are nearly there: ApiConnection already provides public methods to perform arbitrary API actions. The only missing piece is the ability to pass files in those requests, so I would propose to add that.