We still didn't migrate `ci_builds.stage_id`, so we can't use a
belongs_to association. We also have `ci_builds.stage` string attribute,
that we need to phase out in favor of `ci_stages.name`.

Older pipelines can contain jobs without a name, in which case
'nameless' is used right now, so we can properly still handle other
actions on these jobs.

Fixes gitlab-org/gitlab-ce#33403

These were untested by the cherry picked commit.

Not only tracking auto-cancelling in pipelines,
we'll also track this in jobs because pipelines
could be retried and the information would get lost
when this happened. Also erase auto-cancelling
relation for pipelines when they're retried.

This reverts commit e00fb2bdc2090e9cabeb1eb35a2672a882cc96e9.

# Conflicts:
#	.rubocop.yml
#	.rubocop_todo.yml
#	lib/gitlab/ci/config/entry/global.rb
#	lib/gitlab/ci/config/entry/jobs.rb
#	spec/lib/gitlab/ci/config/entry/factory_spec.rb
#	spec/lib/gitlab/ci/config/entry/global_spec.rb
#	spec/lib/gitlab/ci/config/entry/job_spec.rb
#	spec/lib/gitlab/ci/status/build/factory_spec.rb
#	spec/lib/gitlab/incoming_email_spec.rb

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.