Client-side telemetry and Prefix configuration causes excess billing

[jbrantly]

It appears that using the Prefix configuration causes client telemetry to also be prefixed. This in turn seems to cause these metrics to be billable, when the documentation states that they shouldn't be.

Example configuration:

var dogstatsdConfig = new StatsdConfig
{
    StatsdServerName = "127.0.0.1",
    StatsdPort = 8125,
    Prefix = "hr.holo",
    ...
};

These metrics now show up the Volume tab of Metrics:

Non-prefixed datadog.dogstatsd.* metrics do not show up in the Volume tab (but do show up in the Summary tab). Additionally, when looking at metric details, prefixed and non-prefixed report differently:
Non-prefixed

Prefixed

This leads me to believe that the prefixed metrics are being counted as indexed custom metrics and billed accordingly.

According to https://docs.datadoghq.com/developers/dogstatsd/high_throughput/#client-side-telemetry (emphasis mine)

DogStatsD clients send telemetry metrics by default to the Agent. This allows you to better troubleshoot where bottlenecks exist. Each metric is tagged with the client language and the client version. These metrics are not counted as custom metrics.

I do not know if the issue is that the C# client should not be prefixing these, or if they still shouldn't be counted as custom metrics even with the prefix.