Add Shiny for Python to Dashboarding

[chendaniely]

Adding shiny for python as another dashboarding option for Python.

Let me know if I added this correctly. I edited the dashboarding/index.md directly. It didn't seem to follow the same process as adding a tool.

[chendaniely]

Just noticed there's a dashboarding section under all tools. I'll to update the PR:

[chendaniely]

Nvm. it's already listed in all tools 🤦

[jbednar]

Thanks for the contribution!

However, as you can see there were only four main libraries when I wrote this page, and there are now 28 different dashboarding libraries for Python! I don't think it's feasible to say something meaningful and objectively true about all of them, and I cannot see any objective measure (downloads, contributors, star count, etc.) that would justify calling out Shiny in particular compared to the other dozens. So I don't think adding Shiny to the Dashboarding page would be appropriate.

Instead, I think the Dashboarding page should more prominently link to the Dashboarding section of the All Tools page, mention that there are dozens of competing libraries listed there, and then call out some feasible subset as examples, chosen by an objective measure. By popularity (downloads), what seems feasible to me is a cutoff at 100K/month, which gives five to discuss here, adding gradio (and with Bokeh treated separately). If you're interested in making those edits, feel free to repurpose this PR, or else we can close it and I'll open another PR for that purpose.