Aspire CLI - Add to existing solution

### 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.

Right now, using `aspire new` in the CLI creates the project(s) needed, depending on template.

However, this command also adds a new solution, which means the command would not be able to be used in existing solutions.

### Describe the solution you'd like

The command should allow a parameter to add the project(s) it creates to an existing solution.

Bonus: detect if a solution is present and allow the user to select that from the CLI.

### Additional context

_No response_