feat: invoicer contact property for extended profile

Author: Suesswarendieb

ZUGFeRD/InvoiceDescriptor.cs

@@ -219,6 +219,12 @@ public class InvoiceDescriptor
         /// </summary>
         public Party Invoicer { get; set; }
 
+        /// <summary>
+        /// Optional contact only used in Extended profile.
+        /// Detailed contact information of the invoicer BG-X-34
+        /// </summary>
+        public Contact InvoicerContact { get; set; }
+
         /// <summary>
         /// This party is optional and is written in most profiles except Minimum profile
         ///

ZUGFeRD/InvoiceDescriptor23CIIWriter.cs

@@ -856,7 +856,7 @@ public override void Save(InvoiceDescriptor descriptor, Stream stream, ZUGFeRDFo
             _Writer.WriteOptionalElementString("ram", "InvoiceIssuerReference", this._Descriptor.SellerReferenceNo, Profile.Extended);
 
             //   6. InvoicerTradeParty (optional), BG-X-33
-            _writeOptionalParty(_Writer, PartyTypes.InvoicerTradeParty, this._Descriptor.Invoicer, Profile.Extended);
+            _writeOptionalParty(_Writer, PartyTypes.InvoicerTradeParty, this._Descriptor.Invoicer, Profile.Extended, this._Descriptor.InvoicerContact);
 
             //   7. InvoiceeTradeParty (optional), BG-X-36
             _writeOptionalParty(_Writer, PartyTypes.InvoiceeTradeParty, this._Descriptor.Invoicee, Profile.Extended, default, default, this._Descriptor.GetInvoiceeTaxRegistration());