[BUG] Jupyter Notebook links incorrectly point to beta.openai.com instead of platform.openai.com

As a developer browsing the cookbook examples (Jupyter Notebook files), I noticed that some links still point to beta.openai.com, which is no longer a valid domain. These links should be updated to point to platform.openai.com instead.

All links within the Jupyter Notebook files should be reviewed and corrected to ensure they direct to platform.openai.com