Veneur is unable to parse packets from the go dogstatsd client

[marnixbouhuis]

The v1.2 of the DogStatsD protocol introduces a new container ID field: https://docs.datadoghq.com/developers/dogstatsd/datagram_shell/?tab=metrics#dogstatsd-protocol-v12

This extra field is automatically emitted by the official dogstatsd client (added in this PR: https://github.com/DataDog/datadog-go/pull/250).

When veneur tries to parse a packet with this new field it fails with the following error:

time="2022-04-21T12:32:25Z" level=warning msg="Could not parse packet" error="Invalid metric packet, contains unknown section \"c:REDACTED_CONTAINER_ID\"" packet="redacted.redacted:1|c|#some_tag:redacted|c:REDACTED_CONTAINER_ID"