Add an output flag to aspire init

### 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.

When I try to aspirify a existing dotnet solution, the CLI puts the AppHost and ServiceDefaults to the root diretory (or the one with the sln file?).
But my other projects are in a `src` folder.

### Describe the solution you'd like

I want to select where to put these two projects, in the `src` folder for instance.

Something like `aspire init --output src`.

### Additional context

_No response_