Log a warning when EmailDeliveryJob can't find email

This could be a cause of silently failing email notifications so it
makes sense to log this whenever it happens.

Jira-Issue: MAV-3418

Author: stevehook

app/jobs/email_delivery_job.rb

@@ -44,7 +44,13 @@ def perform(
           personalisation.parent&.email
       end
 
-    return if email_address.nil?
+    if email_address.nil?
+      Rails.logger.warn(
+        "Failed to find email address for template #{template_name_sym}, " \
+          "parent #{personalisation.parent&.id}"
+      )
+      return
+    end
 
     template = NotifyTemplate.find(template_name_sym, channel: :email)
     raise UnknownTemplate if template.nil?

spec/jobs/email_delivery_job_spec.rb

@@ -165,6 +165,13 @@
         expect(notifications_client).not_to receive(:send_email)
         perform_now
       end
+
+      it "writes a warning to the logs" do
+        expect(Rails.logger).to receive(:warn).with(
+          /Failed to find email address for template #{template_name}/
+        )
+        perform_now
+      end
     end
 
     context "with a consent form" do