Enable MediaViewer survey on enwiki

Change-Id: Icaa7badf5b38bb048765362d8dc8781c0a7b93ba
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/676
Reduce MediaViewer EventLogging sampling factor

These figures are based on the last 24 hours of data. The goal is to
keep reducing the sampling while maintaining reliable data.

Change-Id: If07080ca138039dcf5de053c0eaa5f2232fa8f13
Merge "Enable MediaViewer survey on enwiki"