add rake tasks for web hooks management

lib/tasks/gitlab/web_hook.rake

+namespace :gitlab do
+  namespace :web_hook do
+    desc "GITLAB | Adds a web hook to the projects"
+    task :add => :environment do
+      web_hook_url = ENV['URL']
+      namespace_path = ENV['NAMESPACE']
+
+      projects = find_projects(namespace_path)
+
+      puts "Adding web hook '#{web_hook_url}' to:"
+      projects.find_each(batch_size: 1000) do |project|
+        print "- #{project.name} ... "
+        web_hook = project.hooks.new(url: web_hook_url)
+        if web_hook.save
+          puts "added".green
+        else
+          print "failed".red
+          puts "  [#{web_hook.errors.full_messages.to_sentence}]"
+        end
+      end
+    end
+
+    desc "GITLAB | Remove a web hook from the projects"
+    task :rm => :environment do
+      web_hook_url = ENV['URL']
+      namespace_path = ENV['NAMESPACE']
+
+      projects = find_projects(namespace_path)
+      projects_ids = projects.pluck(:id)
+
+      puts "Removing web hooks with the url '#{web_hook_url}' ... "
+      count = WebHook.where(url: web_hook_url, project_id: projects_ids, type: 'ProjectHook').delete_all
+      puts "#{count} web hooks were removed."
+    end
+
+    desc "GITLAB | List web hooks"
+    task :list => :environment do
+      namespace_path = ENV['NAMESPACE']
+
+      projects = find_projects(namespace_path)
+      web_hooks = projects.all.map(&:hooks).flatten
+      web_hooks.each do |hook|
+        puts "#{hook.project.name.truncate(20).ljust(20)} -> #{hook.url}"
+      end
+
+      puts "\n#{web_hooks.size} web hooks found."
+    end
+  end
+
+  def find_projects(namespace_path)
+    if namespace_path.blank?
+      Project
+    elsif namespace_path == '/'
+      Project.where(namespace_id: nil)
+    else
+      namespace = Namespace.where(path: namespace_path).first
+      if namespace
+        Project.where(namespace_id: namespace.id)
+      else
+        puts "Namespace not found: #{namespace_path}".red
+        exit 2
+      end
+    end
+  end
+end