Add "suggest url" in DDG onion's manifest

As mentioned here: !178 (comment 2743523)

The onion manifest is missing something like the following for auto-complete:

      "suggest_url": "https://ac.duckduckgo.com/ac/",                                                       
      "suggest_url_get_params": "q={searchTerms}&type=list"

But, before we jump to add this, we need to ask if they actually support auto-complete on their onion.