Only offer to create a future service if the name doesn't already exist

ui-v2/app/controllers/dc/intentions/edit.js

@@ -33,6 +33,9 @@ export default Controller.extend({
     createNewLabel: function(term) {
       return `Use a future Consul Service called '${term}'`;
     },
+    isUnique: function(term) {
+      return !get(this, 'items').findBy('Name', term);
+    },
     change: function(e, value, _target) {
       // normalize back to standard event
       const target = e.target || { ..._target, ...{ name: e, value: value } };

ui-v2/app/templates/dc/intentions/-form.hbs

@@ -8,6 +8,7 @@
               selected=SourceName
               searchPlaceholder='Type service name'
               buildSuggestion=(action 'createNewLabel')
+              showCreateWhen=(action "isUnique")
               oncreate=(action 'change' 'SourceName')
               onchange=(action 'change' 'SourceName') as |service search|
             }}
@@ -27,6 +28,7 @@
               selected=DestinationName
               searchPlaceholder='Type service name'
               buildSuggestion=(action 'createNewLabel')
+              showCreateWhen=(action "isUnique")
               oncreate=(action 'change' 'DestinationName')
               onchange=(action 'change' 'DestinationName') as |service|
             }}