azurerm_orchestrated_virtual_machine_scale_set - fix source_image_id processing

[thefisk]

This is a proposed fix for issue #14820

As discussed in the issue, there is an issue with the azurerm_orchestrated_virtual_machine_scale_set resource, whereby the source_image_id attribute is not sent through to the Azure API. This is a result of an error in the expandOrchestratedSourceImageReference function. We can see on lines 1339-1341 that the function will exit before checking the source_image_id value if the source_image_reference block is empty, which it should be if a source_image_id is provided.

As mentioned, I'm not sure if the prefered fix would be to fix the new function, or simply to make a call to the pre-existing expandSourceImageReference like I have done in this PR. Either way, I figured opening this PR would be a good start to getting this issue resolved as it's been outstanding for 7 months.

[WodansSon]

@thefisk, thank you so much for opening this PR. I am currently working on adding fields to VMSS in PR #17571 and I will pull the fix into that PR to keep everything a bit cleaner. We like to keep the expand and flatten functions separate for Uniform and Orchestrated versions of the VMSS because of the way the service team implements new features into the API. For that reason I will be closing this PR and adding the fix to the existing #17571. Thanks again! 🚀

[thefisk]

Thanks again for confirming, @WodansSon

[github-actions]

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