DEPR: make to_datetime('now') match Timestamp('now')
- [x] closes #18705
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

@jbrockmendel small comment and a rebase and can get this in