Add IResourceBuilder<T> extension method for event subscriptions

[afscrome]

Description

Add a number of extension method on IResourceBuilder<T> to easily subscribe to IDistributedApplicationResourceEvent on a resource

Refactored a few subscription calls over to use the new methods. I can refactor more, just wanted to get a small amount (one per event) to prove the concept out.

Fixes #9168

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected. - Follow up PR to migrate existing uses of .Subscribe<T> over to the new methods
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[afscrome]

cc @DamianEdwards

[davidfowl]

We're trying to decide When* vs On*

[mitchdenny]

Yeah, I think On* already is an established pattern in .NET and I'd prefer not to muddy the waters there anymore (there is already some inconsistency there that we could make worse by doing this with Aspire).

I think what we want is When<T>(...) and WhenEvent(...) which calls When<T>(...).

[Copilot]

Pull Request Overview

This PR introduces a new set of extension methods on IResourceBuilder for event subscriptions and refactors existing subscriptions across various resource builders to use these extensions. Key changes include the creation of new event subscription extension methods, refactoring of subscription calls in SQL Server, Azure, CosmosDB, and custom resource code, and updates to fluent API chaining.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Aspire.Hosting/ResourceBuilderExtensions.cs	Refactored event subscriptions to use the new extension methods.
src/Aspire.Hosting/EventingExtensions.cs	Added new extension methods for event subscriptions.
src/Aspire.Hosting.SqlServer/SqlServerBuilderExtensions.cs	Updated SQL Server resource builder to chain event subscriptions.
src/Aspire.Hosting.Azure.Storage/AzureStorageExtensions.cs	Refactored Azure Storage event subscription calls.
src/Aspire.Hosting.Azure.CosmosDB/AzureCosmosDBExtensions.cs	Refactored CosmosDB subscription and iterated over database collection.
src/Aspire.Hosting.Azure.AIFoundry/AzureAIFoundryExtensions.cs	Updated custom resource subscriptions to use the extension methods.
playground/mongo/Mongo.AppHost/Program.cs	Refactored MongoDB subscription to use the new event extension method.
playground/CustomResources/CustomResources.AppHost/TalkingClockResource.cs	Updated custom resource initialization and event handling.

Comments suppressed due to low confidence (1)

src/Aspire.Hosting/EventingExtensions.cs:15

• The XML documentation for OnBeforeResourceStarted contains an extraneous quotation mark and trailing '/>' at the end. Consider removing these characters for clarity.

    /// Subscribes a callback to the <see cref="BeforeResourceStartedEvent"/> event within the AppHost."/>

[davidfowl]

Formatting here is all messed up.

[davidfowl]

Love it! We can do a follow up to finishing consuming these APIs everywhere

[mitchdenny]

Agree with @davidfowl - this was a good idea @afscrome