Reduce MediaViewer EventLogging rate

Following the launch of Media Viewer to all wikis, we need to reduce
the EventLogging rate of medium-size wikis. The current target is
having less than 1000 daily recorded events per metric per wiki.

Change-Id: I2778942098e87d17f5fb6262e9264c844aa89b2d
Merge "Reduce MediaViewer EventLogging rate"