Add scheduled method to email

Added scheduled method to EmailMicroservice and endpoints to UserController for customers and houses(not working yet). Fixed some issues from the M2 review and updated the class diagram.

core/src/main/resources/prometheus.yml

+global:
+  scrape_interval:     15s
+  evaluation_interval: 15s
+
+# A scrape configuration containing exactly one endpoint to scrape:
+scrape_configs:
+  - job_name: 'prometheus job'
+
+    static_configs:
+      - targets: ['localhost:9090']
+
+  - job_name: 'metrics for electricity microservice'
+    metrics_path: '/actuator/prometheus'
+    scrape_interval: 5s
+    static_configs:
+      - targets: ['smart-energy-management-system-core-service-1:8080']
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