Syncing from upstream OCA/server-env (16.0) - #277

Add a helper to manage the restoring of the database columns when a
module using `server_environment` is uninstalled or the dependency on
`server_environment` is dropped.

Document how to use the helper in an uninstall script or in an upgrade
script (if a new version of the addon drops the dependency).

Helper function typically used for hooks and migration scripts.
Restores database values for fields transitioning to 'server env managed'.

When a field is defined as managed by the server environment, Odoo
ignores the value stored in the database, prioritizing the environment
configuration instead. If no environment configuration exists, the field
may effectively lose its previous value.

This method forces to 'persist' these values if they are not
explicitly overridden by the current environment configuration.

…cation"

To preserve the value of field "smtp_authentication" if we don't set it from
the environment.
Which may happen to anyone updating the sources of mail_environment for its project.

Signed-off-by simahawk