This commit introduces a DefaultEnablement enum that replaces the
"enabledByDefault" boolean flag of Endpoint. This allows to better
control what indicates the default enablement of an endpoint.

With DefaultEnablement#ENABLED, the endpoint is enabled unless an
endpoint specific property says otherwise. With DefaultEnabled#DISABLED,
the endpoint is disabled unless an endpoint specific property says
otherwise. DefaultEnablement#NEUTRAL provides a dedicated option to
indicate that we should resort to the default settings in absence of
a specific property.

See gh-10161