✨ Add support for multiple instance types in AWSManagedMachinePool

[moko-poi]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR adds support for specifying multiple instance types in AWSManagedMachinePool by introducing a new instanceTypes field. This enhancement improves availability, especially when using Spot instances with EKS Managed Node Groups.

Key changes:

• Added new instanceTypes (plural) field to specify a list of instance types
• Retained existing instanceType (singular) field for backward compatibility
• Implemented webhook validation to ensure mutual exclusivity between the two fields
• Added conversion logic between v1beta1 and v1beta2 API versions
• Enhanced launch template validation to reject both fields when launch template is specified

Which issue(s) this PR fixes:
Fixes #3585

Special notes for your reviewer:

• instanceType and instanceTypes are mutually exclusive, enforced by webhook validation
• When converting v1beta2 instanceTypes to v1beta1, the first element is used as instanceType
• Annotation-based conversion data is utilized to preserve state during version conversions
• When launch template is specified, both instanceType and instanceTypes are rejected, consistent with existing validation

Release note:

✨ AWSManagedMachinePool now supports specifying multiple instance types via the new `instanceTypes` field, enhancing Spot instance availability. The existing `instanceType` field remains supported for backward compatibility.

[k8s-ci-robot]

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[k8s-ci-robot]

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[moko-poi]

71efb58
The fix was incorporated based on #4358

[richardcase]

/ok-to-test

[richardcase]

This looks good, thanks @moko-poi .

Just the one comment.

[richardcase]

Lets mark InstanceType as deprecated as well. Long term, we can remove the field and just rely on the InstanceTypes field.