[PROBLEM] Update fine tuning data validation example

[wielandb]

Identify the file to be fixed examples /Chat_finetuning_data_prep.ipynb

Describe the problem Through new things like vision fine-tuning and tool-calls instead of function calls, the validator that one builds in this cookbook is insufficient to check for .jsonl-File validity. Moreover, there seems to be no good resource on all things that invalidate training data. This info is still available in a tedious form, as the fine tuning playground will explain each error to the user.

Describe a solution Update this cookbook to include, ideally, the same checks that the playground performs. It would be helpful so that users can test their jsonl-Files without uploading them.