[13.2 Docs] Add migration guidance for IAzureContainerRegistry obsolete breaking change

[joperezr]

Summary

Aspire 13.2 marks the IAzureContainerRegistry interface as obsolete. Users should migrate to the new ContainerRegistry property on compute environments. There is currently no migration guidance in the reference documentation.

Current State

• The breaking change is mentioned in whats-new/aspire-13-2.mdx under the ""Breaking changes"" section (""IAzureContainerRegistry obsolete"") but with minimal detail.
• The integrations/cloud/azure/azure-container-registry.mdx doc exists but may not reflect the deprecation or the new API pattern.
• No reference documentation explains how to migrate from IAzureContainerRegistry to the new ContainerRegistry property.

What's Needed

1. Expand the breaking change section in whats-new/aspire-13-2.mdx with:

   • Before/after code examples showing old IAzureContainerRegistry usage vs. new ContainerRegistry property
   • Clear explanation of why the interface was deprecated

2. Update azure-container-registry.mdx (if applicable):

   • Mark the old pattern as deprecated
   • Show the new recommended approach using ContainerRegistry on compute environments
   • Add migration steps

3. Add migration guidance to the what's new page or upgrade guide:

   • How to find usages of IAzureContainerRegistry in existing code
   • Step-by-step migration to the new API
   • Timeline for removal (if known)

Context

• Breaking change introduced in Aspire 13.2
• Listed in whats-new/aspire-13-2.mdx section: ""IAzureContainerRegistry obsolete""
• Related doc: integrations/cloud/azure/azure-container-registry.mdx
• Users upgrading from 13.1 to 13.2 will see obsolete warnings and need guidance