ECS_CONTAINER_METADATA_URI_V4 support

[marshall7m]

Just wondering if there's any plans to support v4 of the ecs task metadata endpoint in the near future. Thanks

[keen99]

@marshall7m I think the short answer (2 years later) is that v4 is "as implemented as it's going to get"

that means "learn v4, and implement what you need of it using custom metadata"

which is....a subpar answer. but there ya go:

https://github.com/awslabs/amazon-ecs-local-container-endpoints/blob/mainline/docs/features.md#task-metadata-v4
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