How to configure launch button configuration for new Binder session?

[matthewfeickert]

pyhf is migrating to Jupyter Book v2 in pyhf/pyhf-tutorial#107. In the old (we were very behind on migration) Jupyter Book we could use the following config.yml syntax

# Launch button settings
launch_buttons:
  notebook_interface: jupyterlab
  binderhub_url: https://mybinder.org
  colab_url: https://colab.research.google.com

to create launch buttons in our Jupyter Book that would take users to that notebook in the Jupyter Lab view on mybinder.org or to a Google Colab instance.

For example, https://pyhf.github.io/pyhf-tutorial/SimpleWorkspace.html would allow you to launch to https://mybinder.org/v2/gh/pyhf/pyhf-tutorial/main?urlpath=lab/tree/book/SimpleWorkspace.ipynb or https://colab.research.google.com/github/pyhf/pyhf-tutorial/blob/main/book/SimpleWorkspace.ipynb

In myst.yml I'm unclear on how to do something similar, at least for Binder, as

project:
...
  jupyter:
    binder:
      repo: pyhf/pyhf-tutorial
      ref: main
      provider: github
      url: mybinder.org

yields a launch button, but not one that is able to launch to a particular resource given the binder.repo keys.

From the Myst guide I see that "launch buttons" are experimental (as of PR #2046)

mystmd/docs/website-launch-buttons.md

Lines 10 to 12 in 296ab10

	:::{caution} Launch buttons are experimental!
	We are still learning the best UX and configuration to control launch buttons, so they may change in the future!
	:::

and I also see that (from PR #2110)

mystmd/docs/in-page-execution.md

Lines 90 to 95 in 296ab10

	```{attention} Be aware of multiple keys
	There are two possible locations for `binder` keys:
	1. `project.binder` is for [launch button configuration](./website-launch-buttons.md), and will take the user to a new page with a Binder session.
	2. `project.jupyter.binder` is for in-page computation described here.
	```

indicates I should be using a project.binder key instead of a project.jupyter.binder key, but

project:
...
  jupyter:
  binder:
    repo: pyhf/pyhf-tutorial
    ref: main
    provider: github
    url: mybinder.org

is invalid

⛔️ myst.yml 'binder' must be string (at myst.yml#config.project)

Is it possible to define a Binder launch button capabilities in jupyter-book v2.0.2?

cc @agoose77, @stevejpurves, @choldgraf given this conversation: #2110 (comment)