Adds UTC as select option to timezones select list

no issue

- adds '(GMT) UTC' as select option to available Timezones
- changes default value for active Timezone to 'Etc/UTC'

core/server/data/schema/default-settings.json

@@ -44,7 +44,7 @@
             }
         },
         "activeTimezone": {
-            "defaultValue": "Europe/Dublin",
+            "defaultValue": "Etc/UTC",
             "validations": {
                 "isNull": false
             }

core/server/data/timezones.json

@@ -88,6 +88,10 @@
 			"name": "Atlantic/Cape_Verde",
 			"label": "(GMT -1:00) Cape Verde Is."
 		},
+        {
+            "name": "Etc/UTC",
+            "label": "(GMT) UTC"
+        },
 		{
 			"name": "Africa/Casablanca",
 			"label": "(GMT +0:00) Casablanca, Monrovia"