Update document versioning for PR #724 (#735)

This PR fix the issue of generating docs when we take
https://github.com/microsoft/mscclpp/pull/724 into main branch.
Build docs for main branch separately.
Use HEAD request instead of GET to check if a page exist.
Filter out versions before v0.4.0 in generate_versions.py.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Binyang Li <binyli@microsoft.com>

.github/workflows/doc-build.yaml

@@ -34,5 +34,5 @@ jobs:
           cd docs
           rm -rf doxygen _build py_api
           doxygen
-          make html
+          make multiversion
           touch _build/html/.nojekyll

.github/workflows/gh-pages.yml

@@ -43,7 +43,8 @@ jobs:
           cd docs
           rm -rf doxygen _build py_api
           doxygen
-          make html
+          # Use multiversion target to build all versions
+          make multiversion
           touch _build/html/.nojekyll
       - name: Upload artifacts
         uses: actions/upload-pages-artifact@v3