docs: @InternalApi
    public com.google.bigtable.admin.v2.CreateInstanceRequest toProto(String projectId) {
      builder.setParent(NameUtil.formatProjectName(projectId)).clearClusters();
  
      for (CreateClusterRequest clusterRequest : clusterRequests) {
        builder.putClusters(clusterRequest.getClusterId(), clusterRequest.toEmbeddedProto(projectId));
      }
  
      return builder.build();
    }