ENH: Add 'truncate' option for if_exists arg for DataFrame.to_sql method
This is my first ever PR on an open source project. This one seemed pretty small & straight forward so I gave it go.  Just merged main into the branch so it is conflict free. Please let me know if there's anything else I can do to help get this merged!

See issue #37210 for more context but this essentially gives a user the option to truncate an existing table before inserting new rows into it via the `DataFrame.to_sql` method.

- [X] closes #37210
- [X] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [X] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [X] Added an entry in the latest `doc/source/whatsnew/v2.1.0.rst` file if fixing a bug or adding a new feature.

Amazing!
I was wondering why truncate isn’t supported. > Thanks for the PR, but it's preferred to use a sqlalchemy function to truncate instead of running raw SQL since it's not guaranteed for the SQL to be database dialect agnostic

Thanks @mroeschke ! I couldn't find anything in the SQLalchemy docs for truncate specifically but [they do have](https://docs.sqlalchemy.org/en/20/core/dml.html#sqlalchemy.sql.expression.delete) `.delete()` which would have the same end result of keeping the table but removing all the existing rows. Would that be acceptable function to use for the `truncate` option? I suppose `delete` would work, but possible renaming the option to `delete_rows` would be more appropriate Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.