Poll /metrics for otel metrics

### 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.

We have, as many services do, a /metrics endpoint that exposes metrics.
The metrics aren't pushed, they are pulled by prometheus.
Setting up prometheus and exporting the metrics to aspire dashboard is a lot of work and is hard to maintain.

### Describe the solution you'd like

We would like aspire to poll the /metrics endpoint and pull the metrics actively into the dashboard for a complete dev experience - including testing /metrics integration, and seeing metrics during development without maintaining dev specific code in the service.

### Additional context

_No response_