Hashed storage support for GitLab pages

When hashed storage is enabled, when a project is renamed it doesn't need to be moved on disk. We should update GitLab Pages with support for hashed storage too.

Proposal

Store pages for a project in a hashed location so that it doesn't need to be moved on disk when the project is renamed or transferred.

Links

https://gitlab.com/gitlab-org/gitlab-ce/issues/34489#note_69261016