Create secondary ENI when previous ENI isn't full due to lack of IPs in subnet - enhanced subnet discovery

[jchen6585]

What would you like to be added:
When enhanced subnet discovery is enabled, we should create a secondary ENI using a new subnet (if there is one available) when the previous ENI is failing to add more IPs due to lack of IPs in subnet.

Why is this needed:
This will prevent IPAMD from being stuck trying to allocate IPs to the previous ENI even if the subnet is out of IPs.

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[github-actions]

Issue closed due to inactivity.

[yieon-lyon]

If you provide this method, I think there will be any problems with IP loss for existing instances.
But before understanding this, we must first carefully manage subnet configuration. with cidr ...

[orsenthil]

This is addressed in https://github.com/aws/amazon-vpc-cni-k8s

Edit:
#2954

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[dougbyrne]

I think the previous link was meant to be #2954