github: workflow: docs: Push 'main' docs to gh-pages

WIP to detect pushes to 'main', and push the latest docs to gh-pages.
This currently does the push on any local PR, though.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

.github/workflows/docs.yml

@@ -62,6 +62,11 @@ jobs:
           name: rustdocs
           path: zephyr-lang-rust/rustdocs
 
+      - name: Upload pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: zephyr-lang-rust/rustdocs
+
   doc-publish:
     name: Publish Rust Documentation
     needs: generate-docs
@@ -94,3 +99,20 @@ jobs:
         run: |
           PR_NUM=${{ github.event.number || 'not-a-pr' }}
           aws s3 sync  --only-show-errors . s3://builds.zephyrproject.org/zephyr-lang-rust/pr/$PR_NUM/
+
+  gh-publish:
+    name: Publish main to gh-pages
+    needs: generate-docs
+    permissions:
+      pages: write
+      id-token: write
+    runs-on: ubuntu-24.04
+    # TODO: This "if" should be for main, but need the PR to test.
+    if: |
+      github.event_name = 'pull_request' &&
+      github.repository == 'zephyrproject-rtos/zephyr-lang-rust'
+
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4