Missing request parameters in update quotas

"backup_gigabytes" and "per_volume_gigabytes" parameters
are supported in api v2, they aren't mentioned in api v2
document[1]. On the other hand both of them are mentioned
in api v3 document[2].

[1] https://developer.openstack.org/api-ref/block-storage/
    v2/index.html#update-quotas
[2] https://developer.openstack.org/api-ref/block-storage/
    v3/index.html?highlight=backup_gigabytes#update-quotas
    -for-a-project

Change-Id: I135efd5c2b4735f5821922643926390976453bf5
Closes-bug: #1727631

api-ref/source/v2/parameters.yaml

@@ -293,6 +293,12 @@ backup:
   in: body
   required: true
   type: object
+backup_gigabytes:
+  description: |
+    The size (GB) of backups that are allowed for each project.
+  in: body
+  required: true
+  type: integer
 backup_service:
   description: |
     The service used to perform the backup.
@@ -1265,6 +1271,13 @@ os-vol-tenant-attr:tenant_id:
   in: body
   required: true
   type: string
+per_volume_gigabytes:
+  description: |
+    The size (GB) of volumes in request that are allowed for each
+    volume.
+  in: body
+  required: true
+  type: integer
 perVolumeGigabytes:
   description: |
     The maximum amount of storage per volume, in gibibytes (GiB).

api-ref/source/v2/quota-sets.inc

@@ -98,6 +98,8 @@ Request
    - security_groups: security_groups
    - project_id: quotas_project_id
    - admin_project_id: admin_project_id
+   - backup_gigabytes: backup_gigabytes
+   - per_volume_gigabytes: per_volume_gigabytes
 
 Request Example
 ---------------