Add X-Copy-From-Account to api-ref

While Donagh was kind enough to add Destination-Account in the related
change, we still hadn't documented the PUT-with-X-Copy-From equivalent.

Change-Id: I156ae2d8664873d3f6cc1f742bf950913fd462b0
Related-Change: I315b4e550b7d10880fbc00fce9311127ba609c2d
Closes-Bug: 1367975

api-ref/source/parameters.yaml

@@ -683,6 +683,14 @@ X-Copy-From:
   in: header
   required: false
   type: string
+X-Copy-From-Account:
+  description: |
+    Specifies the account name where the object is copied from. If not
+    specified, the object is copied from the account which owns the new
+    object (i.e., the account in the path).
+  in: header
+  required: false
+  type: string
 X-Delete-After:
   description: |
     The number of seconds after which the system

api-ref/source/storage-object-services.inc

@@ -254,6 +254,7 @@ Request
    - Content-Type: Content-Type_obj_cu_req
    - X-Detect-Content-Type: X-Detect-Content-Type
    - X-Copy-From: X-Copy-From
+   - X-Copy-From-Account: X-Copy-From-Account
    - ETag: ETag_obj_req
    - Content-Disposition: Content-Disposition
    - Content-Encoding: Content-Encoding