Fix a Sidekiq Pro tagging bug (#4933)

Issue: Tags on morgue classes do not properly apply filters when clicked. They redirect to a route that Sidekiq does not service.

Steps to reproduce:
0. Create an app running Sidekiq.
0. Kill a job with a tag.
0. Click on the tag in the web UI.
0. Observe that the tag does not redirect to a route serviced by Sidekiq Rack app. Depending on how host app is configured, route will 404, redirect, or do something else as it falls through.

Root cause:
- It looks like Sidekiq Pro mounts the routes `/filter/dead` but the `display_tags` method links to `/filter/morgue`.

Notes:
- There might be other ways of fixing this problem, like change the `/filter/dead` to `/filter/morgue`. 

Let me know if there's any other info needed or test cases we can provide!

web/views/morgue.erb

@@ -44,7 +44,7 @@
             </td>
             <td>
               <%= entry.display_class %>
-              <%= display_tags(entry, "morgue") %>
+              <%= display_tags(entry, "dead") %>
             </td>
             <td>
               <div class="args"><%= display_args(entry.display_args) %></div>