Update Grape app to Ruby gem 4

Update to the new integration loader mechanism.

ruby/grape/app/Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: /integration
   specs:
-    appsignal (3.9.1)
+    appsignal (4.0.0)
       rack
 
 GEM

ruby/grape/app/api.rb

@@ -1,5 +1,4 @@
 require "grape"
-require "appsignal/integrations/grape"
 
 # In memory database for posts
 class Posts
@@ -24,7 +23,7 @@ def find_by_id(id)
 
 module MyApp
   class BaseAPI < Grape::API
-    insert_before Grape::Middleware::Error, Appsignal::Grape::Middleware
+    insert_before Grape::Middleware::Error, Appsignal::Rack::GrapeMiddleware
   end
 
   module PostsAPI

ruby/grape/app/config.ru

@@ -1,15 +1,12 @@
 require "appsignal"
+require "grape"
 
-Appsignal.config = Appsignal::Config.new(
-  Dir.pwd,
-  ENV.fetch("RACK_ENV", "development")
-)
+use ::Rack::Events, [Appsignal::Rack::EventHandler.new]
+
+Appsignal.load(:grape)
 Appsignal.start
-Appsignal.start_logger
 
 require_relative "api"
 
-use ::Rack::Events, [Appsignal::Rack::EventHandler.new]
-
 MyApp::API.compile!
 run MyApp::API