Have tag operations dialog reflect time machine configuration

If a tag deletion is going to remove images, but those images are not going to be removed immediately, we need to message that

Fixes https://www.pivotaltracker.com/story/show/143063199

endpoints/api/repository.py

@@ -379,6 +379,7 @@ class Repository(RepositoryParamResource):
       'is_starred': is_starred,
       'status_token': repo.badge_token if not is_public else '',
       'trust_enabled': bool(features.SIGNING) and repo.trust_enabled,
+      'tag_expiration_s': repo.namespace_user.removed_tag_expiration_s,
     }
 
     if stats is not None:

static/directives/tag-operations-dialog.html

@@ -122,7 +122,7 @@
 
     <div class="tag-specific-images-view" tag="deleteTagInfo.tag" repository="repository"
          image-loader="imageLoader" style="margin-top: 20px">
-      The following images and any other images not referenced by a tag will be deleted:
+      The following images and any other images not referenced by a tag will be <span ng-if="repository.tag_expiration_s == 0">deleted</span><span ng-if="repository.tag_expiration_s != 0">unavailable and deleted in {{ getFormattedTimespan(repository.tag_expiration_s) }}</span>:
     </div>
   </div>
 

static/js/directives/ui/tag-operations-dialog.js

@@ -153,6 +153,13 @@ angular.module('quay').directive('tagOperationsDialog', function () {
         }, errorHandler);
       };
 
+      $scope.getFormattedTimespan = function(seconds) {
+        if (!seconds) {
+          return null;
+        }
+        return moment.duration(seconds, "seconds").humanize();
+      };
+
       $scope.editLabels = function(info, callback) {
         var actions = [];
         var existingMutableLabels = {};