Create rake task for running this Job

To note - the first time we run this, there's likely to be a massive spike in emails.

To set this in Heroku, we'll need to log into the interface and call it as `rake chaser:three_months`

Signed-off-by: jonathan.kerr <3410350+jonodrew@users.noreply.github.com>

Author: jonodrew

lib/tasks/chaser.rake

@@ -0,0 +1,7 @@
+namespace :chaser do
+  desc "Send emails to users who've not attended in a while"
+
+  task three_months: :environment do
+    SendThreeMonthEmailJob.perform_later
+  end
+end