Description
Creating a new PySpark migration guide sub page and consolidating the existing 9 separate pages into this one new page. This makes it easier to take a look across multiple version upgrades by simply scrolling on the page.
Also, this is similar to the Spark Core Migration Guide page here:
https://spark.apache.org/docs/latest/core-migration-guide.html
Updating the existing main Migration Guide page to point to this new sub page and also making some minor language updates to help readers.