feat: set Table.Schema for permanent external tables (#1701)

Per discussion related to go/bq-external-table-schema

Author: stephaniewang526

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryImpl.java

@@ -286,6 +286,12 @@ public Table create(TableInfo tableInfo, TableOption... options) {
                     ? getOptions().getProjectId()
                     : tableInfo.getTableId().getProject())
             .toPb();
+    // Set schema on the Table for permanent external table
+    if (tablePb.getExternalDataConfiguration() != null) {
+      tablePb.setSchema(tablePb.getExternalDataConfiguration().getSchema());
+      // clear table schema on ExternalDataConfiguration
+      tablePb.getExternalDataConfiguration().setSchema(null);
+    }
     final Map<BigQueryRpc.Option, ?> optionsMap = optionMap(options);
     try {
       return Table.fromPb(

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/it/ITBigQueryTest.java

@@ -1136,6 +1136,28 @@ public void testCreateExternalTable() throws InterruptedException {
     assertTrue(remoteTable.delete());
   }
 
+  @Test
+  public void testSetPermExternalTableSchema() {
+    String tableName = "test_create_external_table_perm";
+    TableId tableId = TableId.of(DATASET, tableName);
+    ExternalTableDefinition externalTableDefinition =
+        ExternalTableDefinition.newBuilder(
+                "gs://" + BUCKET + "/" + JSON_LOAD_FILE, FormatOptions.json())
+            .setSchema(TABLE_SCHEMA)
+            .setConnectionId(
+                "projects/java-docs-samples-testing/locations/us/connections/DEVREL_TEST_CONNECTION")
+            .build();
+    TableInfo tableInfo = TableInfo.of(tableId, externalTableDefinition);
+    Table createdTable = bigquery.create(tableInfo);
+
+    assertNotNull(createdTable);
+    assertEquals(DATASET, createdTable.getTableId().getDataset());
+    assertEquals(tableName, createdTable.getTableId().getTable());
+    Table remoteTable = bigquery.getTable(DATASET, tableName);
+    assertNotNull(remoteTable);
+    assertTrue(remoteTable.delete());
+  }
+
   @Test
   public void testCreateViewTable() throws InterruptedException {
     String tableName = "test_create_view_table";