Fix resource references for default completion models

[joelhulen]

Fix resource references for default completion models

The issue or feature being addressed

Fixes an issue with duplicate GPT4oCompletionAIModel items returning from the AI Model resource provider.

Details on the issue fix or feature implementation

The DefaultCompletionModel resource reference needs to point to the completion-model.json file instead of the completion-4o-model.json file. Also updated the FoundationaLLM agent template to reference the GPT4oCompletionAIModel resource.

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