Instrument task recommendation schemas

Change-Id: Idf2ec7f3c53e795b04c295bea33b8e3f908f05ff
See: https://meta.wikimedia.org/wiki/Research:Task_recommendations#Schemas
Schema:TaskRecommendationImpression is implemented for the post-edit
task recommendation but is blocked on flyout pagination.
Merge "Instrument task recommendation schemas"