Add includePreludeShapes in model plugin

[AndrewFossAWS]

Issue #, if available:
#947

Description of changes:

• Prelude serialization PR: Allow serializing prelude in the node serializer #955
• This PR allows prelude shapes to be included/excluded via the model plugin in smithy-build.json

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mtdowling]

I think you shouldn’t be able to change the default model plugin. Instead, they can use a custom instance of the model plugin using the plugin ID syntax introduced for process plugins “model::withPrelude” and then they can add the new property you introduced here.

So this means:

1. Always overwrite any built-in plugins. This ensures that you can rely on consistent behavior and output no matter the configuration.
2. Use the new plugin ID syntax of "plugin-name::artifact-name". So this becomes "model:modelWithPrelude".

For example, this would work:

{
    "version": "1.0",
    "projections": {
        "source": {
            "plugins": {
                "model::modelWithPrelude": {
                    "includePreludeShapes": true
                }
            }
        }
    }
}

This would be ignored since built-in plugins take precedence.

{
    "version": "1.0",
    "projections": {
        "source": {
            "plugins": {
                "model": {
                    "includePreludeShapes": true
                }
            }
        }
    }
}