TF-2305 Session::getOwnEmailAddress method to fetch the user email address from urn:ietf:params:jmap:principals imip mailto property if not present in the session username, which is the case for Cyrus

model/lib/principals/capability_principals.dart

@@ -0,0 +1,3 @@
+import 'package:jmap_dart_client/jmap/core/capability/capability_identifier.dart';
+
+final capabilityPrincipals = CapabilityIdentifier(Uri.parse('urn:ietf:params:jmap:principals'));