Update DataFrame rsplit() api once pandas rsplit() supports regex

`rsplit` API does not support regex as an argument even though its documentation [does](https://pandas.pydata.org/docs/reference/api/pandas.Series.str.rsplit.html). This issue was [filed](https://github.com/pandas-dev/pandas/issues/29633) a while ago. Once the issue is fixed, update the `rsplit` api once the fix in pandas is released.

Relevant Pandas source code:
* [rsplit](https://github.com/pandas-dev/pandas/blob/v1.4.1/pandas/core/strings/accessor.py#L853-L857) 
* [_str_rsplit](https://github.com/pandas-dev/pandas/blob/60c2940fcf28ee84b64ebda813adfd78a68eea9f/pandas/core/strings/object_array.py#L343)

Imported from Jira [BEAM-14066](https://issues.apache.org/jira/browse/BEAM-14066). Original Jira may contain additional context.
Reported by: yeandy.
Subtask of issue #20958