dcache-frontend: add RESTFUL quota resource

Motivation:

https://rb.dcache.org/r/13089/
master@61a4e8dc4e4877316f3779dfc1a04acd40419067

added the basic user/group quota system to
the namespace.  We wish to export this
as a RESTful resource.

Modification:

The specification for the REST API
(https://docs.google.com/document/d/1gp2IvORqR5N6Jie9d2-EurJZZHNb3Kq1tHMO9A6SYPA/edit#heading=h.c4d58gx2u5nf)
is implemented.

Result:

The quota system is accessible via the frontend.

Target: master
Patch: https://rb.dcache.org/r/13139/
Depends-on: #13135
Requires-book: yes
Requires-notes: yes
Acked-by: Dmitry