Discrepancy between metrics names in prometheus and metadata

Hello,

When creating a Counter metric with client_python 0.4.0 - 0.16.0:

my_metric_count = Counter(name='my_metric_count',
                      documentation='My helpful description',
                      registry=MY_REGISTRY)

The metric will show in prometheus as my_metric_count_total. This is absolutely fine with the world however that same metric will show under http://prometheus:9090/api/v1/metadata as the original name:

    "my_metric_count": [
      {
        "type": "counter",
        "help": "My helpful description",
        "unit": ""
      }
    ],

If one creates the metric with '_total' suffix:

my_metric_count = Counter(name='my_metric_count_total',
                      documentation='My helpful description',
                      registry=MY_REGISTRY)

It will show in prometheus as that exact name my_metric_count_total but the name in the /api/v1/metadata will now be truncated.

    "my_metric_count": [
      {
        "type": "counter",
        "help": "My helpful description",
        "unit": ""
      }
    ],

This breaks certain input plugins with telegraf that rely on the prometheus metadata and remote write to fetch the metric type. Version of this library starting with 0.4.0 exhibit this behavior which is when metrics names began to be munged with '_total' for compatibility with OpenMetrics.

Thank you.

Start by tracing how Counter names are normalized and how metadata is exposed through /api/v1/metadata, using the two examples in the issue as reproductions. Compare the Prometheus exposition name with the metadata key and add regression coverage showing consistent naming for Counters created with and without the _total suffix.