[FIX] fields: copy origin to avoid sharing field objects between registries

Fix a bug introduced in revision f229974, where shared columns objects are
systematically reintroduced in registries.
[FIX] fleet: contract onchange: ensure dict before executing `get`
[FIX] sale_margin: stored field functions cannot trigger other stored field functions

the update of sale.order margin field was trigger with the margin stored field of sale.order.line: This cannot work with the old api
[FIX] website*sale: product_id_change qty is 0 by default

Thus, need to pass the actual quantity to product_id_change in order to set values correctly
[IMP] fields: split the default value from the compute function

This separation allows to set a default value on a related field, for instance.
[FIX] event: jump on the correct menu after installing
the event application (event kanban view).

Also added a missing description on event.type model.
[FIX] doc: branch name in configuration

The branch name is used in the version switcher, so the master branch should have a version of "master".

Maybe the release could be the revision hash? Not sure how to extract it from the repo.
[FIX] website_sale: checkout: do not reset address country every time

Once the value is set it can be modified by the user
(e.g. if geoip detection was wrong), so should not be reset.
[REVERT] typo
Merge remote-tracking branch 'upstream/8.0' into 8.0