[ECS] [request]: allow containers running as non-root to bind to privileged ports

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**Tell us about your request**
The ECS container runtime does not allow a process running as a non-root user to bind to privileged ports (<1024).

So an image designed to serve HTTP traffic either needs to listen on a port other than 80, or to run as root.

The [best practices document](https://docs.aws.amazon.com/AmazonECS/latest/bestpracticesguide/bestpracticesguide.pdf) suggests that I should be running as non-root (p.83) and that it's reasonable to expose port 80 (diagram on p.23). In general I feel one of the advantages of containerisation is the ability to run things on default ports and refer to them by name rather than memorising non-standard ports.

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

**Are you currently working around this issue?**
I'm running some of my containers as root (e.g. the default nginx image) and some as non-root but using a non-privileged, non-standard http port > 1024.

The Docker container runtime, which I suspect is how the majority of image developers test their images and run them locally, now allows privileged port binding for unprivileged users by default: https://github.com/moby/moby/pull/41030

Start by reviewing the ECS container runtime behavior described in the request and compare it with the linked Docker change. Confirm how non-root processes and ports below 1024 are handled, then define support for binding privileged ports without requiring root and verify the behavior across the affected ECS service.

Written by the indexing model from the issue text.