Bug to reproduce
----------------

- Log in as admin
- Go to the frontend page of a course
- Click on 'Add Section'
- Fill the form (name input)
- Press 'Enter' or click on save button x times
x sections with the same name will be created

Specifications
--------------

Prevent the 'Add section' form being submitted multiple times in a row.

task-3432418

closes odoo/odoo#129907

Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>