Migrate hook test dropdown to GlDisclosureDropdown

app/assets/javascripts/pages/admin/hooks/index.js

app/assets/javascripts/pages/projects/hooks/index.js

app/assets/javascripts/webhooks/components/test_dropdown.vue

app/assets/javascripts/webhooks/index.js

app/helpers/hooks_helper.rb

app/views/shared/web_hooks/_hook.html.haml

app/views/shared/web_hooks/_test_button.html.haml

ee/app/assets/javascripts/pages/groups/hooks/index.js

ee/spec/features/groups/hooks/user_tests_hooks_spec.rb

ee/spec/features/groups/settings/webhooks_settings_spec.rb

ee/spec/helpers/ee/hooks_helper_spec.rb

spec/features/admin/admin_hooks_spec.rb

spec/features/projects/settings/webhooks_settings_spec.rb

spec/frontend/webhooks/components/test_dropdown_spec.js

spec/helpers/hooks_helper_spec.rb