[C++][Python] Binary search for sorted tables.

### Describe the enhancement requested

While I support the decision for tables to not have index columns, I have still found it useful to enable fast binary search when it's known that a table is sorted. Currently I'm using `schema.pandas_metadata['index_columns']` to detect sorting. It would be nice if arrow had it own metadata standard, instead of a pandas dependency.

The feature could go through stages:
1. define and document metadata standard
2. `Table.sort_by` adds the metadata
3. a binary search compute function is added

### Component(s)

C++, Python

Start by reviewing the existing Table.sort_by behavior and compute-function entry points, then define the proposed metadata standard independently of pandas. Document the standard, make Table.sort_by add it, and add a binary-search compute function; done means all three stages are specified and implemented for the C++ and Python components.

Written by the indexing model from the issue text.