[Metrics] Getting started document using ostream exporter

[lalitb]

Document Getting started guide for Metrics using Ostream exporter.

Good reference - https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/docs/metrics/getting-started

[marcalff]

In addition to the documentation, and because the ostream exporter is used for tutorials / debugging purpose,
please consider also printing the metric name in the output:

diff --git a/exporters/ostream/src/metric_exporter.cc b/exporters/ostream/src/metric_exporter.cc
index bf97db0..18e73a3 100644
--- a/exporters/ostream/src/metric_exporter.cc
+++ b/exporters/ostream/src/metric_exporter.cc
@@ -96,6 +96,7 @@ void OStreamMetricExporter::printInstrumentationInfoMetricData(
   {
     sout_ << "\n  start time\t: " << timeToString(record.start_ts)
           << "\n  end time\t: " << timeToString(record.end_ts)
+          << "\n  name\t\t: " << record.instrument_descriptor.name_
           << "\n  description\t: " << record.instrument_descriptor.description_
           << "\n  unit\t\t: " << record.instrument_descriptor.unit_;

Thanks.