Publish GitHub pages with explicit GitHub Action Steps (#2461)

This should, if it works, make the exact same website content that we currently have up on https://google.github.io/android-fhir/ appear.

What changes is that instead of GitHub "implicitly" building it for us, via its https://github.com/google/android-fhir/actions/workflows/pages/, we "control" it - which allows us hook our own documentation build steps into it.

All the magic GitHub Workflow Action YAML gobbledygook introduced here is inspired by https://github.com/enola-dev/enola/blob/ed2b1755b9dbf1a0668c86f80048d8bded94de4a/.github/workflows/ci.yaml#L131, where I learnt how to do this to create https://docs.enola.dev.

.github/workflows/build.yml

@@ -96,6 +96,40 @@ jobs:
  path: build.zip
 
  # Steps that follow are related to the Documentation Web Site
+ # This deploys content based on docs/ which ends up in site/
+ # to https://google.github.io/android-fhir/ using GitHub Pages.
 
  - name: Build Docs Site
+ # This 1st step intentionally runs not just on the main ("master") branch
+ # but also for all pull requests. This serves to detect doc breakages.
+ # (But the following steps, which do the actual deploy, only run for
+ # the main branch, of course.)
  run: ./build-docs.bash
+
+ - name: Setup GitHub Pages
+ if: ${{ github.event_name == 'push' }}
+ uses: actions/configure-pages@v4
+
+ - name: Upload site/ directory as GitHub Pages artifact
+ if: ${{ github.event_name == 'push' }}
+ uses: actions/upload-pages-artifact@v3
+ with:
+ path: "site/"
+
+ deploy-website:
+ needs: build
+ if: ${{ github.event_name == 'push' }}
+ runs-on: ubuntu-latest
+ # https://docs.github.com/en/actions/security-guides/automatic-token-authentication
+ # Sets required permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages.
+ permissions:
+ pages: write
+ id-token: write
+ environment:
+ name: github-pages
+ url: ${{ steps.deployment.outputs.page_url }}
+ steps:
+ # https://github.com/actions/deploy-pages
+ - name: Deploy to GitHub Pages
+ id: deployment
+ uses: actions/deploy-pages@v4