DOC (string dtype): update user guide page "Working with text data"

[jorisvandenbossche]

With the new default string dtype in pandas 3.0, we should update the documentation to properly reflect this. The main page about working with string data is https://pandas.pydata.org/pandas-docs/version/2.2/user_guide/text.html

This page currently mentions object dtype vs nullable StringDtype, some differences, and then shows most examples using dtype="string".

We should update that page to reflect that there is now a default "str" dtype, add a historical note about object dtype being the default before pandas 3.0 (and that you can still encounter this, and then how to convert to str dtype; and refer to the upgrade guide), mention the differences of "str" vs "string" dtype, etc

[TEARFEAR]

take