Disable Rack Attack if admin disables it in config file

Grack::Auth already checks this variable. These holdouts were not
disabled, leading to confusion when debugging a customer issue.

config/initializers/rack_attack.rb.example

@@ -17,8 +17,9 @@ paths_to_be_protected = [
 # Create one big regular expression that matches strings starting with any of
 # the paths_to_be_protected.
 paths_regex = Regexp.union(paths_to_be_protected.map { |path| /\A#{Regexp.escape(path)}/ })
+rack_attack_enabled = Gitlab.config.rack_attack.git_basic_auth['enabled']
 
-unless Rails.env.test?
+unless Rails.env.test? || !rack_attack_enabled
   Rack::Attack.throttle('protected paths', limit: 10, period: 60.seconds) do |req|
     if req.post? && req.path =~ paths_regex
       req.ip

config/initializers/rack_attack_git_basic_auth.rb

-unless Rails.env.test?
+rack_attack_enabled = Gitlab.config.rack_attack.git_basic_auth['enabled']
+
+unless Rails.env.test? || !rack_attack_enabled
   # Tell the Rack::Attack Rack middleware to maintain an IP blacklist. We will
   # update the blacklist from Grack::Auth#authenticate_user.
   Rack::Attack.blacklist('Git HTTP Basic Auth') do |req|