- Add two new ActiveRecord models:
  - RootNamespaceStoragestatistics will persist root namespace statistics
  - NamespaceAggregationSchedule will save information when a new update
to the namespace statistics needs to be scheduled
- Inject into UpdateProjectStatistics concern a new callback that will
call an async job to insert a new row onto NamespaceAggregationSchedule
table
- When a new row is inserted a new job is scheduled. This job will
update call an specific service to update the statistics and after that
it will delete thee aggregated scheduled row
- The RefresherServices makes heavy use of arel to build composable
queries to update Namespace::RootStorageStatistics attributes.
- Add an extra worker to traverse pending rows on
NAmespace::AggregationSchedule table and schedule a worker for each one
of this rows.
- Add an extra worker to traverse pending rows on
NAmespace::AggregationSchedule table and schedule a worker for each one
of this rows

The root_ancestor method is heavily used in EE for the group_saml
feature. Having this memoization implemented in CE would eliminate
the need of overriding the root_ancestor method in EE.

- Namespace::Storagestatistics will persist root namespace statistics
- Namespace::AggregationSchedule will save information when a new update
to the namespace statistics needs to be scheduled

Both tables use 'namespace_id' as primary key

This new field will allow to keep track of the storage used by the
packages features, it provides also aggregation at namespace level.

Prepares us for upgrade to Rails 5.2

Model.new.attributes now also returns encrypted attributes.

- Namespace now return avatar_url and web_url
- NamespaceBasic entity was modified to include avatar_url and web_url,
information is fetched differently depending if the Namespace is a user
or a group

Includes documentation changes

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/39858

- Includes instance methods on Group model to detect when a group has
AutoDevOps explicitly/implicitly enabled/disabled.
- Includes migration to add a new column to namespaces table
- Add UI necessary modifications
- Add service and controller to update auto devops
related instances
- Updates project and groups auto devops badges

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52447