🐛 Letting CAPA bypass updating nodegroup version API call for custom AMI

[vishu2498]

What type of PR is this?
/kind bug

What this PR does / why we need it:
The PR fixes an issue when user uses a custom AMI with EKS clusters.

When an EKS cluster is made using a certain k8s version using CAPA and any of the nodegroup's k8s version is lesser than that of cluster's k8s version, CAPA's code has the current flow of making an update nodegroup version API call to update the nodegroup's k8s version until it reaches cluster's k8s version.

But in the case where user specifically providers a custom AMI with lesser k8s version that the cluster in the launch template and wants the AWSManagedMachinePool to stay on the specified k8s version, CAPA complains with the following error:

Message_: "Launch template details can't be null for Custom ami type node group"  

This PR introduces a fix/change that bypasses CAPA to not make update nodegroup version API call and let the nodes get created & join the cluster gracefully.

It is expected from user to always provide custom AMI for nodegroup which has atmost n-1 k8s version of cluster.

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 #

Special notes for your reviewer:

AI Usage:
The PR contains changes done with the help of Cursor & Claude.

Checklist:

• squashed commits
• includes documentation
• includes AI generated content
• includes emoji in title
• adds unit tests
• adds or updates e2e tests

Release note:

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