[16.0] [ADD] shopinvader_sale_channel

[paradoxxxzero]

This module provides a way to link FastAPI endpoints to Sale Channels.

It sets a sale_channel_id in the request context for endpoints linked to a Sale Channel,
and it auto attach Sale Orders created via these endpoints to the corresponding Sale Channel.

In the FastAPI -> FastAPI Endpoints menu, you can now link an endpoint to a
Sale Channel by selecting it in the new Sale Channel field.

Depends on:

• [16.0] [ADD] fastapi_endpoint_context OCA/rest-framework#578