Fix existing resources with the azure publisher

[davidfowl]

Description

• Explore the ExistingAzureResourceAnnotation when looking for parameters.
• Added existing resources to baseline tests

Fixes #8619

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
• Did you add public API?
  • No
• Does the change make any security assumptions or guarantees?
  • No
• Does the change require an update in our Aspire docs?
  • No

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

tests/Aspire.Hosting.Azure.Tests/AzurePublisherTests.cs:46

• [nitpick] Consider extracting the hard-coded resource group 'rg-shared' into a constant or variable to avoid duplication and improve maintainability.

builder.AddAzureStorage("existing-storage").PublishAsExisting("images", "rg-shared");

src/Aspire.Hosting.Azure/AzurePublishingContext.cs:196

• Verify that wrapping the parameter map value in a FunctionCallExpression maintains the intended behavior, as this change alters how the resource group is referenced.

ParameterResource p => new FunctionCallExpression(new IdentifierExpression("resourceGroup"), parameterMap[p].Value.Compile()),

[eerhardt]

LGTM