Merge branch 'add-logging-to-rack-attack' into 'master'

Add logging for rack attack events

Patch for issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/15612 and partial patch for https://gitlab.com/gitlab-com/support/issues/119.

Also related: https://gitlab.com/gitlab-org/gitlab-ce/issues/22527 

Adds logging for throttle and blacklist rack attack events to the production log.

@stanhu @MrChrisW

See merge request !7585

changelogs/unreleased/rack_attack_logging.yml

+---
+title: Add logging for rack attack events to production.log
+merge_request: 
+author: 

config/initializers/rack_attack_logging.rb

+# Adds logging for all Rack Attack blocks and throttling events.
+
+ActiveSupport::Notifications.subscribe('rack.attack') do |name, start, finish, request_id, req|
+  if [:throttle, :blacklist].include? req.env['rack.attack.match_type']
+    Rails.logger.info("Rack_Attack: #{req.env['rack.attack.match_type']} #{req.ip} #{req.request_method} #{req.fullpath}")
+  end
+end