Add missing call for C++/Rust API: `goto-instrument --add-library`

## Description

Add support for the `goto-instrument` option `--add-library` in the C++ and Rust API.

The end result should be facilitating an outcome similar to what is achieved by the call `goto-instrument --add-library b_harness.out b_harness.out'`

## Context

[This is to track items outlined in #7042 that are missing to make the C++ and Rust API more useful]