tags: add index on is_deprecated.

db/migrate/20220410050628_add_is_deprecated_index_on_tags.rb

@@ -0,0 +1,5 @@
+class AddIsDeprecatedIndexOnTags < ActiveRecord::Migration[7.0]
+  def change
+    add_index :tags, :is_deprecated, where: "is_deprecated = TRUE"
+  end
+end