Improve AWSMachinePool diff to default to existing values when comparing launch templates

[cnmcavoy]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Changes how the AWSMachinePool and ASG retrieved from AWS is compared, so that we copy the existing AWSMachinePool values, and compare only fields we manage. This fixes bugs around partially set fields (e.g , MixedInstancesPolicy is set with an instance distribution, but no mixed instance policy) where the AWS defaults do not match the zero-values of fields.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #4070

Special notes for your reviewer:
Split off from #4194

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

Improve AWSMachinePool diff to default to existing values when comparing launch templates.

[k8s-ci-robot]

Hi @cnmcavoy. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[dlipovetsky]

/ok-to-test

[enxebre]

have we considered to default the API explicitly?

[enxebre]

Is this only happening with InstancesDistribution?

[cnmcavoy]

We could default in the webhook, but the default types for some of the fields are not available as types in CAPA, so that would turn this bugfix into an API change. See the discussion here: #4194 (comment)

[enxebre]

/lgtm

[dlipovetsky]

/approve

Thanks for your patience and tenacity, @cnmcavoy! 🙏

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dlipovetsky

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