Fix column rename doc example to reflect correct API

[cabhishek]

• Rename column example in this doc is incorrect.
• This PR updates the example to use update.rename_column(...) instead of update.rename(...).

After PR

with table.update_schema() as update:
    update.rename_column("retries", "num_retries")
    # This will rename `confirmed_by` to `exchange`
    update.rename_column("properties.confirmed_by", "exchange")

[rdblue]

Thanks, @cabhishek! I'll merge when tests are green.

[Fokko]

Thanks @cabhishek for fixing this 🎉