edit ember-can to add additional attribute for namespace

We wanted the ability to get our namespace from query params
in order to do this, we're using additional attributes via
ember-can to set a bound property directly from our
handlebar file. This sets us up better in the event that
the namespace filter changes on the UI because our handlebar
file will be aware of the change, whereas our ability may not
update as the namespace filter updates.

ui/app/abilities/abstract.js

@@ -12,10 +12,6 @@ export default class Abstract extends Ability {
   @not('token.aclEnabled') bypassAuthorization;
   @equal('token.selfToken.type', 'management') selfTokenIsManagement;
 
-  // Pass in a namespace to `can` or `cannot` calls to override
-  // https://github.com/minutebase/ember-can#additional-attributes
-  namespace = 'default';
-
   get _namespace() {
     if (!this.namespace) return 'default';
     if (typeof this.namespace === 'string') return this.namespace;

ui/app/templates/jobs/index.hbs

@@ -12,7 +12,7 @@
     </div>
     {{#if (media "isMobile")}}
       <div class="toolbar-item is-right-aligned">
-        {{#if (can "run job")}}
+        {{#if (can "run job" namespace=this.qpNamespace)}}
           <LinkTo @route="jobs.run" data-test-run-job class="button is-primary">Run Job</LinkTo>
         {{else}}
           <button
@@ -66,7 +66,7 @@
     </div>
     {{#if (not (media "isMobile"))}}
       <div class="toolbar-item is-right-aligned">
-        {{#if (can "run job")}}
+        {{#if (can "run job" namespace=this.qpNamespace)}}
           <LinkTo @route="jobs.run" data-test-run-job class="button is-primary">Run Job</LinkTo>
         {{else}}
           <button