title: Constraint name update in PostgreSQL
body: <p>Is it possible to change the constraint name in Postgres?
  I have a PK added with:</p>
  
  <pre><code>ALTER TABLE contractor_contractor ADD CONSTRAINT commerce_contractor_pkey PRIMARY KEY(id);
  </code></pre>
  
  <p>And I want to to have different name for it, to be consistent with the rest of the system.
  Shall I delete the existing PK constraint and create a new one? Or is there a 'soft' way to 
  manage it?</p>
  
  <p>Thanks! </p>