Merge branch 'pipeline-notifications' into 'master'

app/helpers/notifications_helper.rb

app/mailers/emails/pipelines.rb

app/models/ci/pipeline.rb

app/models/notification_setting.rb

app/models/project_services/pipelines_email_service.rb

app/policies/ci/build_policy.rb

app/policies/ci/pipeline_policy.rb

app/services/ci/send_pipeline_notification_service.rb

app/services/notification_service.rb

...iews/shared/notifications/_custom_notifications.html.haml

app/workers/pipeline_notification_worker.rb

changelogs/unreleased/pipeline-notifications.yml

doc/api/notification_settings.md

doc/workflow/notifications.md

spec/models/ci/pipeline_spec.rb

spec/models/project_services/pipeline_email_service_spec.rb

spec/services/ci/send_pipeline_notification_service_spec.rb

spec/services/notification_service_spec.rb

spec/support/email_helpers.rb

spec/support/notify_shared_examples.rb