SpotInstancePools is sent for non-lowest-price mixed instance allocation strategies

[nathanhuh]

Describe the bug
When mixed_instances_policy.spot_allocation_strategy is set to a non-lowest-price strategy such as price-capacity-optimized, Goployer
still sends SpotInstancePools: 0 to the AWS Auto Scaling API when spot_instance_pools is omitted from the manifest.

AWS rejects the request because SpotInstancePools is only valid with the lowest-price spot allocation strategy.

To Reproduce
Steps to reproduce the behavior:

1. Configure a stack with mixed instances policy enabled.
2. Set spot_allocation_strategy to price-capacity-optimized.
3. Omit spot_instance_pools from the manifest.
4. Deploy the stack.
5. See AWS reject the Auto Scaling request because SpotInstancePools is present with a non-lowest-price allocation strategy.

Example:

mixed_instances_policy:
  enabled: true
  spot_allocation_strategy: price-capacity-optimized
  # spot_instance_pools omitted

Expected behavior
Goployer should omit SpotInstancePools from the AWS request unless spot_allocation_strategy is lowest-price and spot_instance_pools is greater
than zero.

Screenshots
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Additional context
Code-level cause:

pkg/aws/ec2.go always sets SpotInstancePools while building Auto Scaling InstancesDistribution:

SpotInstancePools: aws.Int32(int32(mixedInstancePolicy.SpotInstancePools)),

Because the config struct uses a plain integer, omitted YAML becomes Go's zero value 0. Since the AWS SDK field is a pointer, aws.Int32(0) means
the field is sent as 0, not omitted.

The builder validation only rejects non-lowest-price strategies when spot_instance_pools > 0, so it misses the omitted-value case that still
gets serialized into the AWS request.