Before this commit, when the user shares a portal link, the receiver
has to click on the link to understand what it is about.
This commit uses new key called `preview_object` inside
`portal.frontend_layout` template.
When it is defined, it will add some useful information for the
preview link.
This commit also defines `preview_object` in portal view of project
and task to be able to have the preview link to prevent the user
from having to click on the link to understand what it is about.
task-3186692
closesodoo/odoo#113622
Related: odoo/enterprise#37514
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>