[ECS] [request]: Support PortMappings in Bridge mode on Docker 20.10.6

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**Tell us about your request**
While upgrading to Docker 20.10.6, our team noticed that the port mappings against deployed tasks were no longer behaving the way they had been in 20.10.5.

Prior to upgrading Docker, tasks that had 1 port defined would map to the IPv4 and IPv6 interfaces on the same port. This allowed the targets, registered at the target group layer by ECS, to flow traffic properly into the containers.

After the update to 20.10.6, Docker **fixed** a broken IPv6 configuration in their engine, which now results in 2 random ephemeral port numbers to be applied to Docker containers. This causes Target groups to have split ports and ultimately, if IPv6 is not being supported, half of the traffic to the targets fails out.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
This would help ensure that port mappings defined in task definitions are accurately projected onto the resulting container that is launched, while using the 20.10.6 docker engine.

**Are you currently working around this issue?**
Downgrading to Docker 20.10.5

**Additional context**

**Attachments**
https://github.com/moby/moby/issues/42313

No repository file or test is named; start by reading the linked Moby issue #42313 and the ECS request context around Docker 20.10.6 bridge-mode port mappings. Clarify the implementation scope and validation path before starting; done means task-definition PortMappings are accurately projected to containers without split target-group ports.

Written by the indexing model from the issue text.