Add support for DefaultCooldown options to AWSMachinePool

[randomvariable]

/kind feature
/help

Describe the solution you'd like
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Broken out of #1968

Add support for configuring cooldowns https://docs.aws.amazon.com/autoscaling/ec2/userguide/Cooldown.html to AWSMachinePool

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

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/kind feature
/help

Describe the solution you'd like
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Broken out of #1968

Add support for configuring cooldowns https://docs.aws.amazon.com/autoscaling/ec2/userguide/Cooldown.html to AWSMachinePool

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[arghya88]

/assign

[arghya88]

/lifecycle active