[#3213] Refactoring of HashtagsTableMigrator. Hashtag timeline performance optimization (auto switch to non-aggregate join strategy when efficient).

config/description.exs

@@ -941,6 +941,12 @@ config :pleroma, :config_description, [
         key: :show_reactions,
         type: :boolean,
         description: "Let favourites and emoji reactions be viewed through the API."
+      },
+      %{
+        key: :improved_hashtag_timeline,
+        type: :keyword,
+        description:
+          "If `true` / `:prefer_aggregation` / `:avoid_aggregation`, hashtags table and selected strategy will be used for hashtags timeline. When `false`, object-embedded hashtags will be used (slower). Is auto-set to `true` (unless overridden) when HashtagsTableMigrator completes."
       }
     ]
   },