🐛 Fix ClusterClass MachinePool rollout on BootstrapConfig changes

[bnallapeta]

What this PR does / why we need it:
ClusterClass-managed MachinePools were not triggering node rollouts when BootstrapConfig or InfrastructureMachinePool templates changed. This happened because updateMachinePool() used reconcileReferencedObject() which patches objects in-place without changing their names. Infrastructure providers (like CAPA) watch for configRef.name changes to trigger rollouts, but since the name never changed, no rollout occurred.

This PR changes updateMachinePool() to use reconcileReferencedTemplate() instead. This is the same approach used by updateMachineDeployment().

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 #10496

/area machinepool
/area clusterclass

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[bnallapeta]

@richardcase @AndiDog
Please take a look at this. I am in the process of manually testing this and will write e2e. But, early feedback on the approach will help.

[mpinchover]

Just curious, why are we creating an inline function instead of defining it somewhere else? Not as familiar with Kubernetes code bases so disregard if there there's a good reason.