[FIX] packaging: add missing odoo-mailgate.py

This script is missing in the different Odoo packages.

opw-2008670

closes odoo#34130

Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>

MANIFEST.in

@@ -1,6 +1,7 @@
 include requirements.txt
 include LICENSE
 include README.md
+include odoo/addons/mail/static/scripts/odoo-mailgate.py
 recursive-include odoo *.css
 recursive-include odoo *.csv
 recursive-include odoo *.doc