Add code completion for qweb template contexts using prepared values in controller

[trinhanhngoc]

https://github.com/odoo/odoo/blob/b0be9e074a1ecf1f6de7a03c71df0c63868501e3/addons/website_blog/controllers/main.py#L314

We can use the prepared values in a controller for code completion in the corresponding qweb template.