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

This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points

- we now use the hierarchy class also for epics
- also rename supports_nested_groups? into supports_nested_objects?
  - move it to a concern

Determined by running the script:

```
included = `git grep --name-only ShellAdapter`.chomp.split("\n")
used = `git grep --name-only gitlab_shell`.chomp.split("\n")
included - used
```