Special characters used in the dogstatsd protocol are not escaped in metric name and namespace

[deadok22]

The metric serialization logic replaces special characters used in the dogstatsd protocol in tags, but not in metric namespace and name.

There are similar issues in other dogstatsd client libraries:

• https://github.com/DataDog/java-dogstatsd-client/issues/199
• https://github.com/DataDog/datadog-go/issues/265

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