Add hashtag score for better sorting of autosuggestions (#11427)

* Add hashtag score for better sorting of autosuggestions

* Do not use `~<~` operator with no text_pattern_ops index

db/migrate/20190729185330_add_score_to_tags.rb

@@ -0,0 +1,5 @@
+class AddScoreToTags < ActiveRecord::Migration[5.2]
+  def change
+    add_column :tags, :score, :int
+  end
+end