Update UI for Duo Pro trial errors

ee/app/helpers/trials_helper.rb

...s/gitlab_subscriptions/trials/base_apply_trial_service.rb

...rvices/gitlab_subscriptions/trials/base_create_service.rb

ee/app/views/subscriptions/trials/_form_errors.html.haml

...views/subscriptions/trials/duo_pro/_form_errors.html.haml

...s/subscriptions/trials/duo_pro/step_lead_failed.html.haml

...views/subscriptions/trials/duo_pro/trial_failed.html.haml

ee/app/views/subscriptions/trials/step_lead_failed.html.haml

ee/app/views/subscriptions/trials/trial_failed.html.haml

ee/spec/helpers/trials_helper_spec.rb

.../requests/subscriptions/trials/duo_pro_controller_spec.rb

ee/spec/requests/subscriptions/trials_controller_spec.rb

...gitlab_subscriptions/trials/apply_duo_pro_service_spec.rb

...s/gitlab_subscriptions/trials/apply_trial_service_spec.rb

ee/spec/support/helpers/features/trial_helpers.rb

locale/gitlab.pot