hooks: Add a send_zulip_update_announcements post deploy hook.

This commit adds a post upgrade hook to run the
'send_zulip_update_announcements' management command.

The aim is to improve UX for self hosters by sending
zulip updates as soon as the upgrade completes instead
of waiting for the cron to run.

puppet/zulip/files/hooks/post-deploy.d/send_zulip_update_announcements.hook

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -e
+
+/home/zulip/deployments/current/manage.py send_zulip_update_announcements

puppet/zulip/manifests/app_frontend_once.pp

@@ -2,6 +2,8 @@
 # in a cluster.
 
 class zulip::app_frontend_once {
+  include zulip::hooks::send_zulip_update_announcements
+
   $proxy_host = zulipconf('http_proxy', 'host', 'localhost')
   $proxy_port = zulipconf('http_proxy', 'port', '4750')
   if $proxy_host != '' and $proxy_port != '' {

puppet/zulip/manifests/hooks/send_zulip_update_announcements.pp

@@ -0,0 +1,9 @@
+# @summary Send zuip update announcements after deploy
+#
+class zulip::hooks::send_zulip_update_announcements {
+  include zulip::hooks::base
+
+  zulip::hooks::file { [
+    'post-deploy.d/send_zulip_update_announcements.hook',
+  ]: }
+}