Version warning bar for development part of the documentation

[AlenkaF]

The new released version of the theme is 🔥 Thank you so much for working on it and adding all the cool stuff!

I have a suggestion regarding the new version warning bar that I know would concern Arrow and Pandas project. Maybe others also have a similar situation.

In Arrow, we are referring to the stable version of the docs for all cases except the development part. In the case of the development section, the preferred version of the docs is actually the unstable version. This helps eliminate errors when working on the source code in case of bigger changes in the workflow.

See

• https://arrow.apache.org/docs/developers/contributing.html
• https://arrow.apache.org/docs/12.0/index.html
• https://github.com/apache/arrow/blob/main/docs/source/_static/versionwarning.js

We will use the version warning bar added to the 0.14.0 release of PyData Sphinx Theme (with Arrow 14.0.0 release) and would like to open up a discussion to see if the support of a separate banner text for the developers sections of the documentation is feasible.