chore: add high level classes

Signed-off-by: The one with the braid <the-one@with-the-braid.cf>

test/pkpass_test.dart

@@ -23,17 +23,12 @@ void main() {
   // ignore: unused_local_variable
   final file = PassFile(
     PassMetadata(
-      description: null,
-      formatVersion: 0,
-      organizationName: null,
-      passTypeIdentifier: null,
-      serialNumber: null,
-      teamIdentifier: null,
-      suppressStripShine: null,
-      eventTicket: null,
-      barcode: null,
-      foregroundColor: null,
-      locations: [],
+      description: '',
+      formatVersion: 1,
+      organizationName: '',
+      passTypeIdentifier: '',
+      serialNumber: '',
+      teamIdentifier: '',
     ),
     archive,
   );