Add AKS Prepared Image Specification resource

[benjamin-brady]

Summary

Add the AKS Prepared Image Specification resource as an isolated change on top of dev-containerservice-Microsoft.ContainerService-2026-03.

Included in this PR

• new preparedimagespecification TypeSpec project and generated preview OpenAPI
• prepared image specification examples for create, get, list, update, and delete flows
• companion cspell and suppression updates required for this spec

Notes

• this branch is a clean transplant of the prepared-image-spec work onto the AKS 2026-03 development branch
• kept as a draft so it can be published later when ready

[github-actions]

Next Steps to Merge

Next steps that must be taken to merge this PR:

• ❌ The suppressions added to the AutoRest config files (README.mds) require review. Refer to step 1 in the PR workflow diagram, or to step 3, depending on the kind of suppression you did.

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[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
TypeSpec	Microsoft.ContainerService
Go	sdk/resourcemanager/containerservicepreparedimagespecification/armcontainerservicepreparedimagespecification
JavaScript	@azure/arm-containerservicepreparedimagespecification
Python	azure-mgmt-containerservicepreparedimagespecification
Java	com.azure.resourcemanager:azure-resourcemanager-containerservice-preparedimgspec

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