Support new kwargs `initial` and `where` in reduction functions

### Description

It seems
- `numpy.min()`
- `numpy.amin()`
- `numpy.max()`
- `numpy.amax()`
- ...?

have added additional kwargs `initial` and `where`, but CuPy's counterparts do not. Would be nice to catch up, so opening this issue to track.

ps. I haven't checked if this is a duplicate issue.

### Additional Information

_No response_

Start by comparing CuPy's reduction functions with numpy.min(), amin(), max(), and amax(), then check the corresponding reduction entry points for existing keyword handling. Confirm the intended NumPy semantics for initial and where, and verify that all affected counterparts accept them consistently. Done means the supported reductions match NumPy behavior and have coverage for both new keywords.

Written by the indexing model from the issue text.