Instead of exposing the VisibilityLevel as Integer, expose it as
String `visibility`.

It consolidates these endpoints:
 - /projects
 - /projects/owned
 - /projects/visible
 - /projects/starred
 - /projects/all

Into the /projects endpoint using query parameters.

Follow-up to d05dd81b which changed the nested namespaces in projects
to use API::Entities::Namespace instead of exposing all fields.

Fixes #27730

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

* Use standard helpers for finding group and project

This adds counters for build artifacts and LFS objects, and moves
the preexisting repository_size and commit_count from the projects
table into a new project_statistics table.

The counters are displayed in the administration area for projects
and groups, and also available through the API for admins (on */all)
and normal users (on */owned)

The statistics are updated through ProjectCacheWorker, which can now
do more granular updates with the new :statistics argument.

Allow `order_by` and `sort` parameters to `/api/v3/groups.json`. At
present, only ordering by name and path is supported, and the default
sort is name ascending (alphabetical order).

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

Groups can enable/disable LFS, but this setting can be overridden at the project level. Admin only

Also, mutualize AccessRequests and Members endpoints for Group &
Project.
New API documentation for the AccessRequests endpoints.

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

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb