Expose GOVUK_DATA_SYNC_PERIOD ENV variable for govuk_app_config

This is to enable alphagov/govuk_app_config#160,
which ignores certain exceptions if they occur during the data
sync period. We want to set this via Puppet so that it is DRY and
configured in only one place.

Trello: https://trello.com/c/rAlvGlSp/2123-5-ignore-data-sync-errors-in-govukappconfig

modules/govuk_data_sync_in_progress/manifests/init.pp

@@ -18,11 +18,16 @@
   $fact_path = '/etc/govuk/env.d/FACTER_data_sync_in_progress'
 
   $start_hour = 22
-  $start_minute = 0
+  $start_minute = 00
 
   $finish_hour = 8
   $finish_minute = 00
 
+  govuk::app::envvar { "${title}-GOVUK_DATA_SYNC_PERIOD":
+    varname => "GOVUK_DATA_SYNC_PERIOD",
+    value   => "${start_hour}:${start_minute}-${finish_hour}:${finish_minute}";
+  }
+
   if !defined(File[$fact_path]) {
     file { $fact_path:
       ensure  => present,