backend-app-api: final service to service refactoring

Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

plugins/auth-node/src/types.ts

@@ -389,7 +389,7 @@ export const tokenTypes = Object.freeze({
   limitedUser: Object.freeze({
     typParam: 'vnd.backstage.limited-user',
   }),
-  service: Object.freeze({
-    typParam: 'vnd.backstage.service',
+  plugin: Object.freeze({
+    typParam: 'vnd.backstage.plugin',
   }),
 });