FEATURE: enable tagging by default (#13175)

Over the years we have found that a few communities never discovered tags.

Instead of having them default off we now have them default on, ensuring
that everyone finds out about them.

Co-authored-by: Dan Ungureanu <dan@ungureanu.me>

db/migrate/20210527114834_set_tagging_enabled.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class SetTaggingEnabled < ActiveRecord::Migration[6.1]
+  def up
+    result = execute <<~SQL
+      SELECT created_at
+      FROM schema_migration_details
+      ORDER BY created_at
+      LIMIT 1
+    SQL
+
+    # keep tagging disabled for existing sites
+    if result.first['created_at'].to_datetime < 1.hour.ago
+      execute <<~SQL
+        INSERT INTO site_settings(name, data_type, value, created_at, updated_at)
+        VALUES('tagging_enabled', 5, 'f', NOW(), NOW())
+        ON CONFLICT (name) DO NOTHING
+      SQL
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end