Set custom Apdex for triggerable integrations API

The ".../trigger" endpoints in the integrations API call external
services, so we lower the Apdex urgency to `low` for these endpoints.

https://gitlab.com/gitlab-org/gitlab/-/issues/343602
https://gitlab.com/gitlab-org/gitlab/-/issues/343602#note_716569607

lib/api/integrations.rb

@@ -153,7 +153,7 @@ module API
               requires setting[:name], type: setting[:type], desc: setting[:desc]
             end
           end
-          post "#{path}/#{integration_slug.underscore}/trigger" do
+          post "#{path}/#{integration_slug.underscore}/trigger", urgency: :low do
             project = find_project(params[:id])
 
             # This is not accurate, but done to prevent leakage of the project names