Add privateKeyLocation parameter to the local setup

privateKeyLocation parameter is mandatory for gcloud-pubsub-events
plugin even if it is not used in the local mode. Add privateKeyLocation
to the local setup to avoid exception during the Gerrit startup.

Bug: Issue 14206
Change-Id: Ifdf441a7d0fc849135f55e2e267f1e41182093db
diff --git a/setup_local_env/configs/gerrit.config b/setup_local_env/configs/gerrit.config
index 248f669..58772f0 100644
--- a/setup_local_env/configs/gerrit.config
+++ b/setup_local_env/configs/gerrit.config
@@ -61,5 +61,6 @@
     numberOfSubscribers = 6
+    privateKeyLocation="not used in local mode"
 [plugin "metrics-reporter-prometheus"]
     prometheusBearerToken = token