Add JAXB discriminator to GROUP_INVITE transactions.

src/main/java/org/qora/data/transaction/GroupInviteTransactionData.java

@@ -7,6 +7,7 @@ import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.XmlTransient;
 
+import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorValue;
 import org.qora.transaction.Transaction.TransactionType;
 
 import io.swagger.v3.oas.annotations.media.Schema;
@@ -14,6 +15,8 @@ import io.swagger.v3.oas.annotations.media.Schema;
 // All properties to be converted to JSON via JAXB
 @XmlAccessorType(XmlAccessType.FIELD)
 @Schema(allOf = { TransactionData.class })
+//JAXB: use this subclass if XmlDiscriminatorNode matches XmlDiscriminatorValue below:
+@XmlDiscriminatorValue("GROUP_INVITE")
 public class GroupInviteTransactionData extends TransactionData {
 
 	// Properties