Add resource to environment callback context

[eerhardt]

Description

When setting environment variables on a resource, it is useful to get the resource so you can grab annotations off of it to use in the environment settings.

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?
  • Yes
    • If yes, did you have an API Review for it?
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
• Does the change make any security assumptions or guarantees?
  • No
• Does the change require an update in our Aspire docs?
  • No

[Copilot]

Pull Request Overview

This pull request adds support for passing the resource into environment callback contexts so that environment variable callbacks can access resource annotations. It updates the constructors for EnvironmentCallbackContext across multiple areas and adds tests to verify that the resource is available.

Reviewed Changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
playground/AzureContainerApps/AzureContainerApps.AppHost/Program.cs	Adds a new environment callback that uses the resource to retrieve an annotation.
tests/Aspire.Hosting.Tests/ResourceExtensionsTests.cs	Inserts an assertion that ensures the resource is set in the environment callback.
tests/Aspire.Hosting.Tests/WithEnvironmentTests.cs	Updates callbacks to assert that the resource is not null.
tests/Aspire.Hosting.Tests/ExpressionResolverTests.cs	Adds a check for a non-null resource in an environment variable callback.
src/Aspire.Hosting/ApplicationModel/EnvironmentCallbackContext.cs	Introduces a new constructor and exposes the Resource property with proper null-checking.
src/Aspire.Hosting.Azure/AzureResourcePreparer.cs	Updates the EnvironmentCallbackContext instantiation to include the resource.
src/Aspire.Hosting.Docker/DockerComposePublishingContext.cs	Updates the instantiation to pass the resource into the EnvironmentCallbackContext.
src/Aspire.Hosting.Kubernetes/KubernetesResourceContext.cs	Passes the resource to the EnvironmentCallbackContext in environment processing.
src/Aspire.Hosting.Azure.AppContainers/AzureContainerAppsInfrastructure.cs	Updates environment callback processing to use the new constructor with resource.
src/Aspire.Hosting/ApplicationModel/ResourceExtensions.cs	Changes the instantiation of EnvironmentCallbackContext to correctly include the resource and the environment variables dictionary.

Files not reviewed (2)

• playground/AzureContainerApps/AzureContainerApps.AppHost/api.module.bicep: Language not supported
• playground/AzureContainerApps/AzureContainerApps.AppHost/aspire-manifest.json: Language not supported