beta: Configure $wgStatsdServer and $wgStatsdMetricPrefix

Send statsd packets to labmon1001.eqiad.wmnet and prefix metrics with
'BetaMediaWiki' to make them easy to find and not collide with other
possible Labs MW installs pointed at the same collector.

Bug: T108091
Change-Id: I7d20abbf6515ce1ef18002c0458d27cdc83f7f8a