Subreddit search: Test new rel1 relevancy

Use rel1 relevancy when the subreddit_relevancy feature flag is
enabled. Add activity as a sort option to access original relevancy.

r2/r2/controllers/front.py

@@ -914,6 +914,9 @@ class FrontController(RedditController):
         else:
             include_over18 = True
 
+        if feature.is_enabled('subreddit_relevancy') and sort == 'relevance':
+            sort = 'rel1'
+
         q = SubredditSearchQuery(query, sort=sort, faceting={},
                                  include_over18=include_over18)
 

r2/r2/lib/cloudsearch.py

@@ -1072,13 +1072,15 @@ class SubredditSearchQuery(CloudSearchQuery):
     search_api = g.CLOUDSEARCH_SUBREDDIT_SEARCH_API
     sorts = {
         'relevance': '-activity',
+        'activity': '-activity',
         'rel1': '-rel1',
         'rel2': '-rel2',
     }
     sorts_menu_mapping = {
         'relevance': 1,
-        'rel1': 2,
-        'rel2': 3,
+        'activity': 2,
+        'rel1': 3,
+        'rel2': 4,
     }
 
     known_syntaxes = ("plain",)