Trigger a PR to Dash User Contrib when we make a release

[michaelblyons]

Several other packages¹ have automation to update themselves in Dash User Contributions. It's not too troublesome to do this by hand for now, but why not make it a pipeline for us, too?

Our tagging in Contrib is this repo's version-doc site update date so that changes either to code here or to the underlying source data both advance the version number appropriately.

Footnotes

1. Sample: TLDR Pages' GitHub Action to update its version in Dash User Contrib ↩