Use wikibase-api post() not mw.api.postWithToken()
Take advantage of the wb.api.RepoApi.post() for token addition,
parameter validation and possible user checking
Bug: T209043
Depends-On: Ib69ab313239b62afc5df0dfa1b6149b4ae4d4b80
Change-Id: I3bede1e0d90a0f84c42f1c9863429a8ea66612e1