[ECS] [feature-request]: SELinux official support

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**Tell us about your request**
What do you want us to build?
ECS Container support for SELinux profiles and configuration without overly permissive requirements (privileged / super-privileged).

Docker supports [running containers with security options](https://docs.docker.com/engine/reference/run/#security-configuration)
ECS supports setting these options via the [container definition's DockerSecurityOptions](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_ContainerDefinition.html)

But
Once SELinux has been enabled in the kernel and docker daemon, it’s unclear how to run a container without using privileged mode, (which subverts the whole purpose of using SELinux in the first place.)

Even when using the most permissive SELinux profiles, the overlay storage driver itself seems to require [SELinux to be set to permissive mode (essentially disabling SELinux)](https://github.com/docker/for-linux/issues/791#issuecomment-563231208).

Start with the ECS ContainerDefinition DockerSecurityOptions documentation and the linked Docker security-configuration and overlay storage-driver discussion. Determine the supported SELinux profile and configuration requirements for ECS containers without privileged mode; the issue does not define an implementation entry point or a concrete acceptance test.

Written by the indexing model from the issue text.