[FARGATE] [request]: Image labels are not visible on the metadata endpoint

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**Tell us about your request**
ECS Task definition supports `dockerLabel` map, that adds labels to the container. These labels are visible in the container, if queried from the metadata server (`curl -s 169.254.170.2/v2/metadata | jq .Labels`).

`Dockerfile` supports `LABEL` statements that add labels to the image, when running locally with `docker run`, these labels are assigned to the container (and visible with `docker inspect $container_id`). When running in fargate, these labels are not visible on the metadata server (when queried by `curl -s 169.254.170.2/v2/metadata | jq .Labels`)

**Which service(s) is this request for?**
Fargate. ECS might also be affected by this

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Trying to add additional metadata (git-sha + build version) to metrics collected by 3rd party agent. For example Datadog supports `DD_DOCKER_LABELS_AS_TAGS` option, which allows tagging everything coming out from the agent.

**Are you currently working around this issue?**
Work around would be updating task definition

**Additional context**
I am not the only person to run into this: [this stack exchange question](https://devops.stackexchange.com/questions/6825/docker-image-labels-in-fargate-are-not-applied-to-containers).

Start by reproducing the metadata request against 169.254.170.2/v2/metadata and compare Dockerfile LABEL values with task-definition dockerLabel values. Check the Fargate metadata endpoint behavior; done means image labels are visible in the endpoint's Labels output, including values such as the git SHA and build version.

Written by the indexing model from the issue text.