feat: create manual client for Write API

google-cloud-bigquerystorage/pom.xml

@@ -59,6 +59,10 @@
       <groupId>com.google.api</groupId>
       <artifactId>api-common</artifactId>
     </dependency>
+    <dependency>
+      <groupId>com.google.api</groupId>
+      <artifactId>gax</artifactId>
+    </dependency>
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java</artifactId>

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1alpha2/ProtoSchemaConverter.java

@@ -31,7 +31,12 @@
 public class ProtoSchemaConverter {
   private static class StructName {
     public String getName() {
-      return "__S" + (count++);
+      if (count == 0) {
+        count++;
+        return "__ROOT__";
+      } else {
+        return "__S" + (count++);
+      }
     }
 
     private int count = 0;