Add C# / `DistributedApplicationTestingBuilder` API to access telemetry data

### 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.

Aspire recently added the telemetry api for accessing telemetry from the dashboard. It would be nice if this was cleanly exposed via `DistributedApplicationTestingBuilder`.

### Describe the solution you'd like

I (well copilot) have an initial stab at an API at https://github.com/microsoft/aspire/issues/17802

For streaming it relies on `IAsyncEnumerable` which provides a really nice API for consuming telemetry from .Net, although that may not translate well to polyglot.

There is also a bit of a pit of failure int hat the api won't work until you enable the dashboard, so ideally there should be a fail fast path that clearly fails when the dashboard is unavailable, and advise how to start the dashboard.

### Additional context

_No response_