Revert "Remove newrelic gem. Closes #12860"

This reverts commit 53176717.

Conflicts:
	Gemfile.lock

Gemfile

@@ -303,6 +303,8 @@ group :production do
   gem "gitlab_meta", '7.0'
 end
 
+gem "newrelic_rpm", '~> 3.14'
+
 gem 'octokit', '~> 3.8.0'
 
 gem "mail_room", "~> 0.6.1"

Gemfile.lock

@@ -479,6 +479,7 @@ GEM
     net-ldap (0.12.1)
     net-ssh (3.0.1)
     netrc (0.11.0)
+    newrelic_rpm (3.14.1.311)
     nokogiri (1.6.7.2)
       mini_portile2 (~> 2.0.0.rc2)
     nprogress-rails (0.1.6.7)
@@ -960,6 +961,7 @@ DEPENDENCIES
   nested_form (~> 0.3.2)
   net-ssh (~> 3.0.1)
   nokogiri (~> 1.6.7, >= 1.6.7.2)
+  newrelic_rpm (~> 3.14)
   nprogress-rails (~> 0.1.6.7)
   oauth2 (~> 1.0.0)
   octokit (~> 3.8.0)

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