[ECS FARGATE] [request]: sysctl support for vm.max_map_count

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**Tell us about your request**
We want to increase the value of `vm.max_map_count` in ECS Fargate containers, ideally in a similar way like the other [system controls](https://aws.amazon.com/blogs/containers/announcing-additional-linux-controls-for-amazon-ecs-tasks-on-aws-fargate/).

**Which service(s) is this request for?**
ECS Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We're running a headless Chrome browser on ECS Fargate Linux 1.4.0, having the browser crashing due to lack of memory. By further investigation we were able to tell the low value (65530) of `vm.max_map_count` to be the culprit. When running on EC2 there was no problem with value of 1048576; once decreased to 65530 we were able to reproduce the problem.
An alternative of switching to EC2 is costly and has more maintenance overhead.

**Are you currently working around this issue?**
Switching to EC2.

**Additional context**
Chromium team is aware of the [issue](https://issues.chromium.org/issues/364804214).
Similar requests for raising `vm.max_map_count` were posted in #460.

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