Description
We hardcode that API docs always should show h1 - h3 in the right table of contents, whereas the default is to only show h2 - h3.
We do this because it's useful for API class pages, where it's nice to have the class name show up in the right table of contents. That's useful as a way to quickly jump to the class definition because it is non-trivial, like including the constructor and class docstring.
However, that is a bad default for module pages like https://docs.quantum.ibm.com/api/qiskit/exceptions where the page title is not very informative.
Instead, for module pages, we should keep the default of h2 being the min level to show. We should also show h4 because these module pages often have nested information that is worth rendering, although we need to preview a few pages to see what this looks like and confirm it's a good heuristic.