[ENG-10167] 2.1.6 BE: add link header to guid metadata endpoints (#11594)

* add link header to guid metadata endpoints for registry and project

* update code

Author: mkovalua

website/views.py

@@ -423,4 +423,8 @@ def guid_metadata_download(guid, resource, metadata_format):
 def metadata_download(guid):
     format_arg = request.args.get('format', 'datacite-json')
     resource = Guid.load(guid)
-    return guid_metadata_download(guid, resource=resource, metadata_format=format_arg)
+    is_resource_project_or_registration = isinstance(resource.referent, (Node, Registration))
+    response = guid_metadata_download(guid, resource=resource, metadata_format=format_arg)
+    if is_resource_project_or_registration:
+        response.headers['link'] = f'<{settings.DOMAIN}{guid}/>; rel="describes"; type="text/html"'
+    return response