Fix missing Mastodon/PosgreSQL backups

The backup cookbook was incomplete, and also there was no database
configured to be backed up.

site-cookbooks/kosmos-mastodon/recipes/default.rb

@@ -180,10 +180,18 @@ application mastodon_path do
   end
 end
 
+#
+# Backup
+#
+
 unless node.chef_environment == "development"
-  # Backup the database to S3
   node.override["backup"]["postgresql"]["host"]     = "localhost"
   node.override["backup"]["postgresql"]["username"] = "postgres"
   node.override["backup"]["postgresql"]["password"] = node['postgresql']['password']['postgres']
+  unless node["backup"]["postgresql"]["databases"].include? 'mastodon'
+    node.override["backup"]["postgresql"]["databases"] =
+      node["backup"]["postgresql"]["databases"].to_a << "mastodon"
+  end
+
   include_recipe "backup"
 end