aspire-apphost-singlefile template contains legacy apphost.run.json

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

Starting with Aspire 13.2, aspire.config.json became the preferred unified configuration file, replacing the `apphost.run.json` with `aspire.config.json`. The release notes also note that launch profiles previously stored in `apphost.run.json` are now merged into `aspire.config.json`.

However, newly created Aspire projects from the current templates still include both the new `aspire.config.json` file without profiles and the old `apphost.run.json` file with profiles.

For context, we work on file-based/single-file apphost support in [JetBrains/aspire-plugin](https://github.com/JetBrains/aspire-plugin) and would like to deprecate the legacy configuration format in favor of the new `aspire.config.json`

### Expected Behavior

Aspire file-based/single-file apphost templates generate a project with the new `aspire.config.json` configuration file format.

### Steps To Reproduce

Generate a new project with the command below

```console
dotnet new aspire-apphost-singlefile
```

### Exceptions (if any)

_No response_

### Aspire doctor output

_No response_

### Anything else?

_No response_

Start by running `dotnet new aspire-apphost-singlefile` and inspect the generated configuration files in the template output. Find the template source for `aspire-apphost-singlefile`, then verify how launch profiles are represented. Done means the generated project uses `aspire.config.json` with the profiles and no legacy `apphost.run.json`.

Written by the indexing model from the issue text.