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/k8s/dev/emailnotifierjob.yaml

@@ -0,0 +1,42 @@
+apiVersion: batch/v1
+kind: CronJob
+metadata:
+  name: emailnotifierjob
+spec:
+  schedule: "*/5 * * * *"
+  concurrencyPolicy: Forbid
+  successfulJobsHistoryLimit: 3
+  failedJobsHistoryLimit: 3
+  jobTemplate:
+    spec:
+      template:
+        metadata:
+          labels:
+            app: emailnotifierjob
+        spec:
+          serviceAccountName: default-service-account
+          nodeSelector:
+            cloud.google.com/gke-spot: "true"
+          restartPolicy: Never
+          containers:
+          - name: emailnotifierjob
+            image: "emailnotifierjob"
+            resources:
+              requests:
+                memory: "52Mi"
+                cpu: 50m
+              limits:
+                memory: "52Mi"
+                cpu: 50m
+            env:
+            - name: "GCP_PROJECT"
+              value: "flowy-dev-440017"
+            - name: "AERO_ADDR"
+              value: "aero:50051"
+            - name: "PUSHER_GRPC_ADDR"
+              value: "pusher:50051"
+            - name: "LLINK_POSTGRES_CONNECTION_URL"
+              valueFrom:
+                secretKeyRef:
+                  name: shared-secrets
+                  key: LLINK_POSTGRES_CONNECTION_URL