While Fleet config files are typically named `fleet.yaml`, the recent
introduction of user-driven bundle scanning enables a config file to be
named arbitrarily, in which case it must still be excluded from the
corresponding bundle. Fleet now takes care of this without any action
needed from the user.

Integration tests also demonstrate that `.fleetignore` files can be
leveraged to exclude config files living in the same directory as
the config file referenced explicitly through user-driven bundle
scanning. Fleet would otherwise not exclude those files from the bundle.