We need a handler for Google Cloud Vision's image labeling API. Note that there is an official client library that we should probably use:
https://cloud.google.com/vision/docs/libraries#client-libraries-install-php
Related:
https://cloud.google.com/vision/docs/detecting-labels
https://cloud.google.com/vision/docs/supported-files
Note that ultimately this will have to deal with the Google->Wikidata concept mapping that is yet to be created (T229678). Still, we can get the basic pieces in place now.