Allow users to select manifest schema version when creating or updating

[ryfu-msft]

Description of the new feature / enhancement

As more manifest schema versions come out, Winget-Create should still support previous manifest schema versions either when generating a new manifest or updating their existing manifest.

This may even imply having an experimental feature setting that can be turned on to try creating newer versions of a schema early.

Proposed technical implementation details

This could be set using a CLI argument like --schema and having the model used to generate the model change depending on the selected schemaVersion.

The experimental feature would require an additional field to be added to the settings schema to enable early access to newer schema versions.