✨ Support storing Ignition user data in S3 bucket for AWSMachinePool

[AndiDog]

What this PR does / why we need it:

Reopened from #5172 because of branch issues.

EC2 user data is insecure and very limited in size (16 KB). Use the S3 bucket storage also for machine pools. The difference to AWSMachine is that the S3 objects must stay around because a new instance could be started by the ASG at any time, and user data with a valid token must exist. Both a lifecycle policy for regular deletion, and explicit S3 object deletion requests, are used for cleanup, so that normally, only 1-3 launch template versions' user data are stored in S3. Each launch template version relates to one S3 object.

What type of PR is this?

/kind feature

Which issue(s) this PR fixes:

Didn't find an existing issue. My company ran into EC2 user data size limit problems.

Special notes for your reviewer:

This change has been successfully used in the Giant Swarm fork of CAPA since July 2024, on production clusters. I have adapted the change to the latest upstream changes, in particular the introduction of IgnitionStorageTypeOption (#4700) and made sure the previous default storage type is kept. Therefore, I retested this feature using Tilt on a plain CAPI@main + CAPA@main setup, with AWSCluster + Flatcar AMI + AWSMachinePool in my manifests.

Checklist:

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

Release note:

Support storing Ignition user data in S3 bucket for `AWSMachinePool`

[k8s-ci-robot]

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[AndiDog]

/test pull-cluster-api-provider-aws-test

[AndiDog]

/test pull-cluster-api-provider-aws-e2e

[k8s-ci-robot]

@AndiDog: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-aws-e2e	4a31f81	link	false	/test pull-cluster-api-provider-aws-e2e

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