Added user password hash relation

Necessary to aid in managing password hashes for users.

Milestone: minor

app/relations/user_password_hash.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module Terminus
+  module Relations
+    # The user password hash relation.
+    class UserPasswordHash < DB::Relation
+      schema :user_password_hash, infer: true
+    end
+  end
+end