ECS Fargate detection changes

[jtduffy]

The updated agent spec details the new requirements for reporting an ECS fargate docker id. Specifically:

• The ECS fargate endpoint must be checked, even if a docker id was found using cgroups
• If found, it must reported as a new vendor in the utilization payload (details in the spec)
• Both the cgroup docker id and ECS fargate docker id will be reported if both are present

The metadata environment variables which specify the endpoints are unchanged, as is the order in which to check them (ie: check the v4 endpoint prior to checking the un-versioned endpoint). The response JSON is also unchanged.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-311489