Integrate email notifications into signup and login (#38)

backend/product/config.example.yml

@@ -31,3 +31,9 @@ api:
       token_length: 32
       check:
         min_length: 12
+  notifications:
+    address: localhost:8443
+    token_env: SXCHNGE_NOTIFICATIONS_TOKEN
+    ca_file: ../notifications/tls/ca.pem
+    server_name: localhost
+    activation_url: http://localhost:5126/verify-email