If the type of a configuration field is a package, show the name of its
package *variable* as the default value.
* gnu/services/configuration.scm (generate-documentation){show-default}
{package->symbol}: New nested procedures. Use them to format the field
entries.
Co-authored-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>