insertSeederRegistration function
Adds '<name>': <className>.new, to the seeders map in file.
Returns the updated file, or null when the seeder is already registered
or the seeders map can't be found.
Implementation
String? insertSeederRegistration(
String file, {
required String name,
required String className,
}) => insertRegistryEntry(
file,
variable: 'seeders',
type: 'Seeder Function()',
key: name,
value: '$className.new',
);