External contributors (and namely Odoo PS) forget to set the author
field in their manifest file. The result is that the module is wrongly
registered with `'author': 'Odoo S.A.'`.
This work makes the field mandatory, with a warning when not set. It
also offers an upgrade-code script to mass-rewrite all the manifests in
order to set the author.
task-4485983
closesodoo/documentation#11956
Related: odoo/odoo#196408
Related: odoo/enterprise#78513
Related: odoo/design-themes#1044
Signed-off-by: Julien Castiaux (juc) <juc@odoo.com>