[FIX] document_page_approval: Add Change Request Manager rule

Steps to reproduce the error:
- Modify the content of a page (with a different user).
- Go to the Change request menu and Cancel the change.
- Click on the "Back to draft" button.
- An error will be displayed

TT55569

document_page_approval/views/document_page_approval.xml

@@ -45,6 +45,7 @@
                         type="object"
                         string="Back to draft"
                         invisible="(not am_i_owner or not am_i_approver) and (state not in ('cancelled', 'to approve'))"
+                        groups="document_page.group_document_manager"
                     />
                     <field name="am_i_owner" invisible="1" />
                     <field name="am_i_approver" invisible="1" />