Allow `WaitForCompletion` with multiple replica instances

[JamesNK]

Is there an existing issue for this?

• [X] I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

WaitForCompletion doesn't work when the dependency has multiple replicas: https://github.com/dotnet/aspire/blob/05cbb1cf5e446d5e6fd0c5ebac63fa708af3f964/src/Aspire.Hosting/ApplicationModel/ResourceNotificationService.cs#L188-L191

Describe the solution you'd like

When all replicas have started, wait for completion should be true.

Additional context

No response