Docsy upgrade including Bootstrap v5

[chalin]

• A core contribution to Major update of Docsy and Bootstrap #2419
• More changes will follow, but this seems ready for fielding
• Main OTel-specific change was to rework the registry form and entry display:
  • Note: entry description markdown is now rendered in the original entry list. I still need to fix the fuse.js-generated entries, as noted in Ensure that fuse.js-generated registry entries also render markdown in descriptions #2491

⚠️ NOTE: website contributors should run the following commands after this PR gets merged:

$ nvm use
$ npm install

@svrnm @cartermp - I've walked through most of the site and addressed all problems or created a corresponding issue. PTAL. Note that slight layout changes are to be expected, a result of Bootstrap style tweaks.

Preview: https://deploy-preview-2490--opentelemetry.netlify.app/

[svrnm]

clicked through a few pages, all looks good, @chalin please merge if you think you're ready

[chalin]

I've added a note to the opening comment to remind contributors to run at least npm install after this PR lands. If they don't they'll get an error message.