Fix update of Template properties

Pre-requisite :

• install template rendering addon https://connect.nuxeo.com/nuxeo/site/marketplace/package/nuxeo-template-rendering
• create a non-admin user and grant him Write access to /default-domain/templates

Steps to reproduce

1. As the non admin user, navigate to Defaut Domain > Templates
2. Click the + icon and choose File Template
3. Set the Title and click on the Create button
4. Go to Template Configuration tab
5. Click on Edit
6. For the field "Target Document Types", change the value and set it to "File"
7. Click on the Save button
8. Observe that nothing happens

When looking at the Network tab in the Developer tools, there is a HTTP 404 with this response

{"entity-type":"exception","status":400,"message":"Cannot set the value of property: dc:creator since it is readonly"}

The bug is probably due to the changes introduced by NXP-27137

Expected behavior:
The template is saved with its changes.