Interface for miscellaneous [class@Session] features.
SessionFeature is the interface used by classes that extend the functionality of a [class@Session]. Some
features like HTTP authentication handling are implemented internally via `SoupSessionFeature`s. Other features can be added to the
session by the application. (Eg, [class@Logger], [class@CookieJar].)
See [[email protected]_feature], etc, to add a feature to a session.