Ensure DogStatsD source has full support for Origin Detection.

[tobz]

Context

The DogStatsD source must have full support for Origin Detection, which includes:

• container ID extension (e.g., counter:1|c|c:acdea168264a08f9aaca0dfc82ff3551418dfd22d02b713142a6843caa2f61bf for resolved container IDs, or counter:1|c|c:in-1273114 for container cgroup controller inode)
• entity ID tag (e.g., counter:1|c|#dd.internal.entity_id:7e87a71f-5f07-4d4f-8560-d7dbe666c66b)
• UDS-based peer socket credentials (uses SO_PEERCRED to get the process ID of the sending client, which is then resolved to the container ID it belongs to)
• External Data extension (stringified list of additional origin attributes, e.g. counter:1|c|e:it-false,cn-nginx,pu-3413883c-ac60-44ab-96e0-9e52e4e173e2)

In scope

• Collecting all possible sources of origin entity data and storing them on Metric

Out of scope

There's a number of very related items that are out of scope for this particular issue, but will be addressed separately as a follow-up.

• Resolving non-container IDs to container IDs
• Ensuring that enrichment behavior matches the Datadog Agent

Work items

(non-exhaustive, living list)

• Add support for External Data-based origin detection in the DogStatsD codec. #162