Move trials controller/view layer to gitlab_subscriptions module

.rubocop.yml

.rubocop_todo/gitlab/strong_memoize_attr.yml

...todo/layout/line_end_string_concatenation_indentation.yml

.rubocop_todo/rails/strong_params.yml

.rubocop_todo/rspec/factory_bot/avoid_create.yml

.rubocop_todo/rspec/named_subject.yml

.rubocop_todo/style/inline_disable_annotation.yml

app/views/groups/show.html.haml

...scripts/pages/gitlab_subscriptions/trials/create/index.js

...avascripts/pages/gitlab_subscriptions/trials/new/index.js

...pp/assets/javascripts/pages/subscriptions/trials/index.js

ee/app/controllers/gitlab_subscriptions/trials_controller.rb

ee/app/helpers/gitlab_subscriptions/trials_helper.rb

ee/app/helpers/trials_helper.rb

ee/app/views/gitlab_subscriptions/trials/_alert.html.haml

.../views/gitlab_subscriptions/trials/_form_errors.html.haml

...pp/views/gitlab_subscriptions/trials/_lead_form.html.haml

...lab_subscriptions/trials/_select_namespace_form.html.haml

ee/app/views/gitlab_subscriptions/trials/step_lead.html.haml

...ws/gitlab_subscriptions/trials/step_lead_failed.html.haml