ui: Fix sticky namespace selector (#11830)

When adding a namespace via the UI, the app model which contains a list
of namespace isn't refreshed. This means when we use the same list after
adding a namespace to search for the namespace that is contained in the
URL, if that namespace in the URL is the new one, its is not found, and
therefore the menu does not get 'selected' properly, leaving a default
selection of 'default'

This commit instead uses peekAll of the Ember Data store to access the
entire list of cached namespaces instead of using the now stale
app.nspaces one.

.changelog/11830.txt

@@ -0,0 +1,4 @@
+```release-note:bug
+ui: Fixes an issue where under some circumstances the namespace selector could
+become 'stuck' on the default namespace
+```

ui/packages/consul-ui/app/routes/dc.js

@@ -26,20 +26,19 @@ export default class DcRoute extends Route {
   @service('repository/dc') repo;
   @service('repository/nspace/disabled') nspacesRepo;
   @service('settings') settingsRepo;
+  @service('store') store;
 
   async model(params) {
-    const app = this.modelFor('application');
-
     let [token, nspace, dc] = await Promise.all([
       this.settingsRepo.findBySlug('token'),
       this.nspacesRepo.getActive(),
-      this.repo.findBySlug(params.dc, app.dcs),
+      this.repo.findBySlug(params.dc, this.store.peekAll('dc')),
     ]);
     // if there is only 1 namespace then use that
     // otherwise find the namespace object that corresponds
     // to the active one
-    nspace =
-      app.nspaces.length > 1 ? findActiveNspace(app.nspaces, nspace) : app.nspaces.firstObject;
+    const nspaces = this.store.peekAll('nspace');
+    nspace = findActiveNspace(nspaces, nspace);
 
     let permissions;
     if (get(token, 'SecretID')) {