feat: send email notifications for missed messages

- New cron job in cluster
- Handle presence and other concerns
- Toggle in app to disable email notifications
- Handles other edge cases such as cooldown period
- Simple html email with simple message

Closes #117

go/Makefile

@@ -46,7 +46,7 @@ migrate-prod:
 	SKAFFOLD_DEFAULT_REPO=$(PROD_REPO) skaffold run -p migrations --kube-context prod --tail
 
 # ---- Deploy ----
-# Use MODULE=orion or MODULE=worker or MODULE=pusher to deploy a single service, e.g.:
+# Use MODULE=orion or MODULE=worker or MODULE=pusher or MODULE=emailnotifierjob to deploy a single service, e.g.:
 #   make deploy-dev MODULE=orion
 
 .PHONY: deploy-dev