Add specs for new parameter and updated documentation as well.

CE: Update sort options for issues list

See merge request gitlab-org/gitlab-ce!31849

Update capitalization in /administration, /api, /ci
and /customization

Increase sort options for issues list from updated_at and create_at,
to include more options close to what is required in actual issue list
UI.

This helps us to use REST API for issues list with sorting capabilities

https://gitlab.com/gitlab-org/gitlab-ce/issues/57402

Root namespaces have storage statistics.
This commit allows namespace owners to get those stats via GraphQL
queries like the following one

{
  namespace(fullPath: "a_namespace_path") {
    rootStorageStatistics {
      storageSize
      repositorySize
      lfsObjectsSize
      buildArtifactsSize
      packagesSize
      wikiSize
    }
  }
}

- Adds `searchBy` util in common utils
- Adds placeholder `SidebarItemEpicsSelect`

Deletes extra spaces and line, makes lists consistent, and
fixes links.

Add a new method to `Api.js`: `projectUsers`

See merge request gitlab-org/gitlab-ce!31801

Update api_resources docs - remove incorrect group vulnerabilities reference

See merge request gitlab-org/gitlab-ce!31979