[ECS/EC2] [request]: ENI Trunking as a requirement for attribute-based instance type selection

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**Tell us about your request**

ENI Trunking is supported on a subset of instance types: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/container-instance-eni.html#eni-trunking-supported-instance-types
I would like to be able to use [Attribute-based instance type selection](https://docs.aws.amazon.com/autoscaling/ec2/userguide/create-asg-instance-type-requirements.html) when creating my autoscaling group, but I want it to only select instance types that would allow me to pack more tasks per host. The current `NetworkInterfaceCount` requirement I don't think would work - I am more looking for a `RequireENITrunkingSupport` or even something like `NetworkInterfaceCountPerMemoryMiB` (though would the count reflect the with- or without-ENI-trunking-support limit?)

**Which service(s) is this request for?**
ECS and EC2

**Are you currently working around this issue?**
Manually maintaining a list of allowed instance types. Currently the list is maintainable but I would like to not have to keep it up to date as new instance types come around. Also that first link of supported instance types shows there are some exceptions to some instance type families, so I would like to not have to keep up with that list either.

Start by reading the AWS documentation linked in the request for ENI Trunking supported instance types and attribute-based instance type selection. The request is complete when AWS defines a supported way to require ENI Trunking during instance selection, including how the relevant network interface limits are evaluated.

Written by the indexing model from the issue text.