[BACKPORT] rke2 machineSelectorFiles.fileSources have multiple duplicate entries

[matttrach]

Backport #1426 to provider v5 targeting Rancher v1.9x.

[matttrach]

#1441 merged

[Josh-Diamond]

Ticket #1438 - Test Results - ✅

Verified on Rancher v2.9.3 with Rancher2 v5.2.0-rc1:

Scenario	Test Result	Result
1.	Provision downstream RKE2 AWS Node driver cluster => edit cluster and force reconciliation => confirm no duplicate entries are seen in machineSelectorFiles.fileSources	✅

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Scenario 1 - ✅

1. Provision a downstream RKE2 AWS Node driver cluster
2. Once active, modify snapshot_retention and apply changes
3. Once cluster updates and is active, edit YAML of cluster object and verify machineSeletorFiles.fileSources
4. Verified - No duplicates seen in machineSelectorFiles.fileSources after cluster update; as expected