AWSMachinePool minSize should be allowed to go to 0

[mweibel]

/kind bug

What steps did you take and what happened:
I tried to set the AWSMachinePool minSize to 0 but this failed to apply

The current validation rule of AWSMachinePoolSpec.minSize specifies a validation rule of Minimum=1.
An ASG does not have such a minimum and therefore allows setting minSize to zero.

It might (depending on the implementation) also be important for the autoscaler scale to zero proposal, to have this validation corrected.

What did you expect to happen:
Setting minSize: 0 works and updates the autoscaling group accordingly.

Anything else you would like to add:
Happy to provide a PR for this, if that sounds like something you'd accept :) Not sure what kind of tests would be needed to do so - would need some guidance there.

Environment:

• Cluster-api-provider-aws version: v1.3.0
• Kubernetes version: (use kubectl version): 1.23

[richardcase]

/triage accepted
/priority important-longterm
/help

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@richardcase:
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In response to this:

/triage accepted
/priority important-longterm
/help

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[richardcase]

When doing this we should also update the e2e tests to test scale to 0.

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[mweibel]

/remove-lifecycle stale