Hadrian Reppas

GH-46897: [Docs][C++][Python] Fix asof join documentation

2

### Rationale for this change The asof join documentation is currently incorrect. Here is a copy of https://github.com/apache/arrow/issues/46897 for convenience: There are two issues with the asof join docs: 1....

### Describe the bug, including details regarding any error messages, version, and platform. There are two issues with the asof join docs: 1. In the doc for the `on` parameter,...