[IMP] developer: add "widget" attr to cohort field tag

Related PR: https://github.com/odoo/enterprise/pull/46693

task-3475463

closes #6284

Related: odoo/enterprise#46693
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

Author: auon-odoo

content/developer/reference/user_interface/view_architecture.rst

@@ -3411,6 +3411,8 @@ attributes:
     units, e.g. € and $).
     If the value is a domain, the domain is evaluated in the context of the current row's
     record, if ``True`` the corresponding attribute is set on the cell.
+  ``widget`` (optional)
+    alternate representations for a field's display.
 
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