Defer adding of GraphQL middleware

This is so that we don't autoload GitlabSchema in our
initializer which ends up autoloading all our GraphQL
related classes.

This causes a very long deprecation message in Rails 6

config/initializers/graphql.rb

@@ -6,6 +6,8 @@ GraphQL::Field.accepts_definitions(authorize: GraphQL::Define.assign_metadata_ke
 GraphQL::Schema::Object.accepts_definition(:authorize)
 GraphQL::Schema::Field.accepts_definition(:authorize)
 
-GitlabSchema.middleware << GraphQL::Schema::TimeoutMiddleware.new(max_seconds: ENV.fetch('GITLAB_RAILS_GRAPHQL_TIMEOUT', 30).to_i) do |timeout_error, query|
-  Gitlab::GraphqlLogger.error(message: timeout_error.to_s, query: query.query_string, query_variables: query.provided_variables)
+Gitlab::Application.config.after_initialize do
+  GitlabSchema.middleware << GraphQL::Schema::TimeoutMiddleware.new(max_seconds: ENV.fetch('GITLAB_RAILS_GRAPHQL_TIMEOUT', 30).to_i) do |timeout_error, query|
+    Gitlab::GraphqlLogger.error(message: timeout_error.to_s, query: query.query_string, query_variables: query.provided_variables)
+  end
 end