migrate docusaurus to v3 and add search for documentation

[aalves08]

Summary

Fixes #12653

Occurred changes and/or fixed issues

• migrate docusaurus to v3
• add search for documentation (search index will only happen in build... won't work in dev mode)

Technical notes summary

https://docusaurus.io/docs/migration/v3 + https://docusaurus.io/community/resources#search + https://github.com/lelouch77/docusaurus-lunr-search + https://www.npmjs.com/package/docusaurus-lunr-search

Areas or cases that should be tested

• test all of the relevant commands, yarn docs:install, yarn docs:start, yarn docs:start and yarn docs:serve (this serves the built assets and the search can be tested)

Areas which could experience regressions

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes

[aalves08]

FYI @nwmac @richard-cox