feat: add initials field type (#1279)

Adds a new field type that enables document recipients to add
their `initials` on the document.

packages/lib/types/document-audit-logs.ts

@@ -233,6 +233,10 @@ export const ZDocumentAuditLogEventDocumentFieldInsertedSchema = z.object({
 
     // Organised into union to allow us to extend each field if required.
     field: z.union([
+      z.object({
+        type: z.literal(FieldType.INITIALS),
+        data: z.string(),
+      }),
       z.object({
         type: z.literal(FieldType.EMAIL),
         data: z.string(),