Fix 404s of Thebe files

[Eric-Arellano]

Problem

When using the jupyter-sphinx extension, we get 404s for some missing files. This is due to jupyter/jupyter-sphinx#163.

We actually don't really like the jupyter-sphinx extension anymore and are trying to get rid of it. But still the majority of Qiskit projects use it, so this is probably worth fixing.

How to reproduce

Build the docs with tox -e docs.

Then start up a web server to render the docs with python3 -m http.server -d example_docs/docs/_build/html. It will print to the console what website to go to, I think localhost:8000. It is useful to build the docs with a server because it fixes a bunch of errors you'd normally see in the Developer Console.

Then, open up the Developer Console and look at the 404 errors.

Proposed solution

See jupyter/jupyter-sphinx#163 (comment) and what it links to at sphinx-doc/sphinx#6241 (comment).

I believe you will want to add that code snippet to qiskit_sphinx_theme/__init__.py. In the file's setup function, add a line like this:

qiskit_sphinx_theme/qiskit_sphinx_theme/translations.py

Line 27 in bb3083e

app.connect('config-inited', extend_html_context)

But the event is 'html-page-context', not 'config-inited'.