add sub merchant business client id

Author: tl-tai-tang

src/main/java/com/truelayer/java/payments/entities/submerchants/BusinessClient.java

@@ -12,6 +12,7 @@
 @EqualsAndHashCode(callSuper = false)
 public class BusinessClient extends UltimateCounterparty {
     private final Type type = Type.BUSINESS_CLIENT;
+    private String id;
     private String tradingName;
     private String commercialName;
     private String url;

src/test/java/com/truelayer/java/acceptance/PaymentsAcceptanceTests.java

@@ -864,6 +864,7 @@ private static Stream<Arguments> provideSubMerchantsScenarios() {
                 Arguments.of(
                         "BusinessClient",
                         BusinessClient.builder()
+                                .id("client-123")
                                 .tradingName("Test Trading Ltd")
                                 .commercialName("Test Commercial Name")
                                 .url("https://example.com")

src/test/java/com/truelayer/java/integration/PaymentSubMerchantsIntegrationTest.java

@@ -57,6 +57,7 @@ void shouldDeserializePaymentWithSubMerchants() {
         assertTrue(ultimateCounterparty.isBusinessClient());
 
         BusinessClient businessClient = ultimateCounterparty.asBusinessClient();
+        assertEquals("client-123", businessClient.getId());
         assertEquals("Example Trading Ltd", businessClient.getTradingName());
         assertEquals("Example Commercial Name", businessClient.getCommercialName());
         assertEquals("https://example.com", businessClient.getUrl());

src/test/java/com/truelayer/java/payments/entities/submerchants/SubMerchantsTest.java

@@ -17,6 +17,7 @@ void canCreateBusinessClient() {
                 .build();
 
         BusinessClient businessClient = UltimateCounterparty.businessClient()
+                .id("client-123")
                 .tradingName("Test Trading Name")
                 .commercialName("Test Commercial Name")
                 .url("https://example.com")

src/test/resources/__files/payments/200.get_payment_by_id.with_submerchants.json

@@ -51,6 +51,7 @@
   "sub_merchants": {
     "ultimate_counterparty": {
       "type": "business_client",
+      "id": "client-123",
       "trading_name": "Example Trading Ltd",
       "commercial_name": "Example Commercial Name",
       "url": "https://example.com",