Add a section that contrasts Add and With extension methods on Hosting Integrations

[alistairmatthews]

Summary

Adds a new section to the Integrations Overview article that contrasts and clarifies the behavior of methods starting with "Add" from those starting with "With". Without this clarification, developers may pass unexpected object types to consuming projects when the call WithReference.

Fixes #4736

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Internal previews

📄 File	🔗 Preview link
docs/fundamentals/integrations-overview.md	.NET Aspire integrations overview

[Copilot]

Pull Request Overview

This PR adds documentation to clarify the distinction between Add* and With* extension methods in Aspire hosting integrations. The changes help developers understand the different behaviors and return types of these methods to avoid passing incorrect resource objects when using WithReference.

Key changes:

• Added a new section explaining the pattern and purpose of Add* vs With* methods
• Included code examples demonstrating common pitfalls and correct usage patterns
• Added important callout about passing correct resource objects to client integrations

[IEvangelist]

Hey @copilot please correct these build errors:

Line 709: [Warning] Cross reference not found: 'Aspire.Hosting.EventingExtensions.OnInitializeResource*'.
Line 710: [Warning] Cross reference not found: 'Aspire.Hosting.EventingExtensions.OnBeforeResourceStarted*'.
Line 711: [Warning] Cross reference not found: 'Aspire.Hosting.EventingExtensions.OnConnectionStringAvailable*'.
Line 712: [Warning] Cross reference not found: 'Aspire.Hosting.EventingExtensions.OnResourceEndpointsAllocated*'.
Line 713: [Warning] Cross reference not found: 'Aspire.Hosting.EventingExtensions.OnResourceReady*'.

Simply replace these references in the docs/whats-new/dotnet-aspire-9.4.md file with the following xrefs:

<xref:Aspire.Hosting.DistributedApplicationEventingExtensions.OnInitializeResource*>
<xref:Aspire.Hosting.DistributedApplicationEventingExtensions.OnBeforeResourceStarted*>
<xref:Aspire.Hosting.DistributedApplicationEventingExtensions.OnConnectionStringAvailable*>
<xref:Aspire.Hosting.EventingExtensions.OnResourceEndpointsAllocated*>
<xref:Aspire.Hosting.DistributedApplicationEventingExtensions.OnResourceReady*>