Incorrect AMI when flexible to both arm64 and amd64

[ellistarn]

Version

Karpenter: v0.3.4 (unreleased, only at HEAD)

Kubernetes: v1.0.0

Expected Behavior

When instance types are flexible to both arm and amd, Karpenter should correctly launch instances of either kind.

Actual Behavior

We aren't currently smart enough to pick two launch templates and separate the requests to EC2 (we just pick one). One way to solve this would be to call EC2 twice, but this is a bit tricky since we don't currently have any semantic aware retry logic in the cloud provider (and instead do retries in the outer loop). Fleet doesn't support specifying launch template as an override.

Simplest path forward:

1. Default to just [amd64] in defaulting logic
2. If customer specifies [amd64, arm64], separate the instance types and only call fleet with a subset (default amd64?)

Steps to Reproduce the Problem