Allow the dashboard to be added to an existing project

While the whole project is amazing (seriously, kudos), the Dashboard on it's own is pretty good, and reminds me of Glimpse back in the day.

What would be great is if users of existing applications that aren't considered an "Aspire App" could add the dashboard when running locally.

If there was an extension like:

```csharp
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddAspireDashboard();

var app = builder.Build();
```

Everyone could benefit.

What I'd see that doing is.

* Add an OTLP exporter for `http://localhost:18889`
* Add that exporter for Logs, Metrics and Traces
* Add the Dashboard as a hosted service

We could add configuration for ports, and also disable some UI elements that aren't relevant. It would also be great if you could tail the logs too (too many people don't know how to find the log tail in Visual studio and it's useful).

I've mocked it up, and will push a nuget to my Github feed, happy to take suggestions on whether you'd want to take the dashboard in this direction. It's really hacky right now to get around some limitations on internal classes, but it does the job.

My biggest concern with this is that people see it as something they can deploy to prod, and it becomes a security risk, however, if it's limited to Web, we could force it to not work when the environment is production to help people into that pit of success.

https://github.com/martinjt/aspire-app-extension