Update docs on publishing to GitHub Pages

Example 2 on the docs site for publishing to github pages https://docs.antora.org/antora/latest/publish-to-github-pages/#github-actions-workflow should be updated.

• The tagged release of kameshsampath/antora-site-action@v0.2.4 uses Antora 2.3.4 instead of 3.0.0 or 3.0.1
• There kameshsampath/antora-site-action@master does use 3.0.0 but is broken with the lunr search capability turned on as it then tries to use the old generator with 3.0.0
• I have created a fork of the action and a pull request to kameshsampath at bfranske/antora-site-action@master which bumps to Antora 3.0.1 and uses the new lunr extension however I am unsure if the PR will be accepted as it appears kameshsampath may not be maintaining the action anymore per Sept 26, 2021 comment on https://github.com/kameshsampath/antora-site-action/pull/7

It may be worth eliminating this example entirely and suggesting people use example 3 instead. My testing seems to indicate that using a GitHub action which uses the Antora Docker image only runs about 2 seconds faster than downloading and installing directly from NPM in the workflow like example 3.

Example 3 could use a little update too. In particular it would be useful to show how to use Lunr directly with Github actions NPM. See my example at https://github.com/bfranske/ihitc-docs/blob/main/.github/workflows/publish2.yml note that in my example I have commented out the actual publishing of the built files to Github Pages just so I could time it building the site compared to the Docker image based workflow like Example 2.