[docs]: Default behaviour of ConfigDrive is unclear

# Documentation request

https://cloudinit.readthedocs.io/en/latest/reference/datasources/configdrive.html reads:

> By default, cloud-init always considers this source to be a fully-fledged datasource. Instead, the typical behavior is to assume it is really only present to provide networking information.

This describes what cloud-init "always" does in opposition to its "typical behaviour", leaving it unclear what cloud-init's actual default behaviour is.