[16.0][ADD] website_event_sale_seat_reserve

[cyrilmanuel]

This module allows to make a pre-reserve on registrations after creating a draft order from website. If a customer add a registration to his cart, the registration will create a draft order and will be automatically pre-reserved.

superseed of https://github.com/OCA/event/pull/396

depends of :

https://github.com/OCA/event/pull/456 https://github.com/OCA/event/pull/457

[github-actions[bot]]

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