Add dormant New Relic gem

The gem can be enabled and configured via environment variables.

CHANGELOG

@@ -2,6 +2,7 @@ v 7.3.0
   - Always set the 'origin' remote in satellite actions
   - Write authorized_keys in tmp/ during tests
   - Use sockets to connect to Redis
+  - Add dormant New Relic gem (can be enabled via environment variables)
   - Expire Rack sessions after 1 week
   - Cleaner signin/signup pages
   - Improved comments UI

Gemfile

@@ -251,3 +251,5 @@ end
 group :production do
   gem "gitlab_meta", '7.0'
 end
+
+gem "newrelic_rpm"

Gemfile.lock

@@ -296,6 +296,7 @@ GEM
     net-scp (1.1.2)
       net-ssh (>= 2.6.5)
     net-ssh (2.8.0)
+    newrelic_rpm (3.9.4.245)
     nokogiri (1.6.2.1)
       mini_portile (= 0.6.0)
     nprogress-rails (0.1.2.3)
@@ -641,6 +642,7 @@ DEPENDENCIES
   minitest (~> 5.3.0)
   mousetrap-rails
   mysql2
+  newrelic_rpm
   nprogress-rails
   omniauth (~> 1.1.3)
   omniauth-github

config/newrelic.yml

+# New Relic configuration file
+#
+# This file is here to make sure the New Relic gem stays
+# quiet by default.
+#
+# To enable and configure New Relic, please use
+# environment variables, e.g. NEW_RELIC_ENABLED=true
+
+production:
+  enabled: false
+
+development:
+  enabled: false
+
+test:
+  enabled: false