Reduce EventLogging sampling rate for MediaViewer

Another pass of reducing the EL sampling for MediaViewer,
based on the data for the past 24 hours.
The goal is to keep individual events per wiki below or
around 1000 records per day.

Change-Id: Ia87d8fb1b50bcf320c2a9b8dd9597820189da3ef
Merge "Reduce EventLogging sampling rate for MediaViewer"