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.

首先跟踪 Counter 名称如何被规范化，以及 metadata 如何通过 /api/v1/metadata 暴露，并使用 issue 中的两个示例作为复现。比较 Prometheus exposition name 与 metadata key，并添加回归覆盖，展示使用和不使用 _total 后缀创建的 Counter 的命名一致性。