Updated users API documentation
Moved API level changes to the service level

This forks live at https://github.com/gitlabhq/default_value_for/tree/69-fix-action_controller-parameters-handling
and fixes an issue where default_value_for wouldn't handle
`ActionController::Parameters` correctly with Rails 5.

This fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/54093

.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Partially addresses #47424.

The initializers including this were doing so at the top level, so every object
loaded after them had a `current_application_settings` method. However, if
someone had rack-attack enabled (which was loaded before these initializers), it
would try to load the API, and fail, because `Gitlab::CurrentSettings` didn't
have that method.

To fix this:

1. Don't include `Gitlab::CurrentSettings` at the top level. We do not need
   `Object.new.current_application_settings` to work.
2. Make `Gitlab::CurrentSettings` explicitly `extend self`, as we already use it
   like that in several places.
3. Change the initializers to use that new form.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

This param is passed to service in two places, one is in the build_user for non ldap oauth users. And the other is in the initial production admin user seed data.

Without this change, when setting up GitLab in a production environment, you were not being given the option of setting the root password on initial setup in the UI.

Signed-off-by: Rémy Coutable <remy@rymai.me>