impl(bq_driver): Picosecond support

Author: Khushikathuria008

google/cloud/bigquery/v2/minimal/benchmarks/benchmarks_config.cc

@@ -359,6 +359,12 @@ google::cloud::StatusOr<JobConfig> JobConfig::ParseArgs(
   flags_.push_back(
       {"--use-int64-timestamp=", "outputs timestamp as usec int64",
        [this](std::string const& v) { use_int64_timestamp = (v == "true"); }});
+  flags_.push_back(
+         {"--timestamp-output-format=", 
+          "sets timestamp output format",
+          [this](std::string const& v) {
+              timestamp_output_format = v;
+          }});
   flags_.push_back(
       {"--min-creation-time=",
        "min job creation time. If set, only jobs created after or at this "

google/cloud/bigquery/v2/minimal/benchmarks/benchmarks_config.h

@@ -100,6 +100,7 @@ struct JobConfig : public Config {
   int start_index = 0;
   int timeout_ms;
   bool use_int64_timestamp;
+  std::string timestamp_output_format;
 
   bigquery_v2_minimal_internal::Projection projection;
   bigquery_v2_minimal_internal::StateFilter state_filter;

google/cloud/bigquery/v2/minimal/internal/job_request.cc

@@ -343,6 +343,7 @@ std::string DataFormatOptions::DebugString(absl::string_view name,
                                            int indent) const {
   return internal::DebugFormatter(name, options, indent)
       .Field("use_int64_timestamp", use_int64_timestamp)
+      .Field("timestamp_output_format",timestamp_output_format)
       .Build();
 }
 

google/cloud/bigquery/v2/minimal/internal/job_request.h

@@ -313,12 +313,14 @@ struct DataFormatOptions {
   DataFormatOptions() = default;
   bool use_int64_timestamp = false;
 
+  std::string timestamp_output_format = "FLOAT64";
   std::string DebugString(absl::string_view name,
                           TracingOptions const& options = {},
                           int indent = 0) const;
 };
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(DataFormatOptions,
-                                                use_int64_timestamp);
+                                                 use_int64_timestamp, 
+                                                timestamp_output_format);
 
 // Indicates the type of compute mode for the query stage.
 //