feat: Use author-tools for iddiff instead of rfcdiff at www (ietf-tools#4834)

Author: rjsparks

ietf/settings.py

@@ -542,7 +542,7 @@ def skip_unreadable_post(record):
 
 # no slash at end
 IDTRACKER_BASE_URL = "https://datatracker.ietf.org"
-RFCDIFF_BASE_URL = "https://www.ietf.org/rfcdiff"
+RFCDIFF_BASE_URL = "https://author-tools.ietf.org/iddiff"
 IDNITS_BASE_URL = "https://author-tools.ietf.org/api/idnits"
 IDNITS_SERVICE_URL = "https://author-tools.ietf.org/idnits"