[docsy] Enable site search

[chalin]

Google Custom Search Engine (GCSE) approach:

• Setup GSC: https://search.google.com/search-console?resource_id=sc-domain%3Atheupdateframework.io
• Enable GCSE. For details, see Configure search with a Google Custom Search Engine
  • Enable search over entire website
  • Note GCSE ID: 06ecafa260afd40f9
• Configure Hugo + Docsy to use new GCSE - #92
• Ensure that the GCSE ID is recognized as a non-profit. (WIP)

In case we can't get GCSE to work with the site's CSP, we should consider alternatives.

• Support offline search. For options, see https://www.docsy.dev/docs/adding-content/search/

[chalin]

Putting this on hold until I confirm whether or not GCSE is usable with unsafe-eval prohibited.