Add ability to purge undeliverable domains from admin interface (#16686)

app/controllers/admin/instances_controller.rb

app/helpers/admin/action_logs_helper.rb

app/models/admin/action_log_filter.rb

app/policies/instance_policy.rb

app/services/purge_domain_service.rb

app/views/admin/instances/show.html.haml

app/workers/admin/domain_purge_worker.rb

config/locales/en.yml

config/routes.rb

spec/controllers/admin/instances_controller_spec.rb

spec/policies/instance_policy_spec.rb

spec/services/purge_domain_service_spec.rb

spec/workers/admin/domain_purge_worker_spec.rb