ENH: consistency of input args for boundaries (pd.date_range)
closes #43394 

xref #40245
- [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

is this *also* closing https://github.com/pandas-dev/pandas/issues/43394 ? e.g. a bug fix, if so this needs a separate note  > is this _also_ closing #43394 ? e.g. a bug fix, if so this needs a separate note

What do you mean by separate note by the way? go ahead and rebase this https://github.com/pandas-dev/pandas/pull/43504/checks?check_run_id=3612446736

couple of tests that need addressing (you can either assert the future warning or just change closed -> inclusive in the test) some comments & can you merge master. ping on green. thanks @zyc09 