feat: signing order (#1290)

Adds the ability to specify an optional signing order for documents.
When specified a document will be considered sequential with recipients
only being allowed to sign in the order that they were specified in.

apps/marketing/src/app/(marketing)/singleplayer/client.tsx

@@ -168,6 +168,7 @@ export const SinglePlayerClient = () => {
     sendStatus: 'NOT_SENT',
     role: 'SIGNER',
     authOptions: null,
+    signingOrder: null,
   };
 
   const onFileDrop = async (file: File) => {