Add support for aspire add to create proj references

### 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.

I am trying to add references for my project to my app host - Ideally, I should be able to do this the same way I add an integration

### Describe the solution you'd like

```aspire add``` could take a relative path as a local project integration e.g

```ps
aspire add ./MyProject.App
```

### Additional context

_No response_