fixes a bug where nginx will crash if eos goes into diagnostic mode a… (#1506)

fixes a bug where nginx will crash if eos goes into diagnostic mode after service init has completed

backend/src/nginx/diagnostic-ui.conf

@@ -1,3 +1,9 @@
+
+map $http_upgrade $connection_upgrade {
+        default upgrade;
+        '' $http_connection;
+}
+
 server {
         listen 80 default_server;
         listen [::]:80 default_server;