mdbx-ci: build github-pages by doxygen.

Change-Id: I9d84ca299cf0b8579157f84dae42fcbb09a6f8bc

.github/workflows/doxygen-github-pages.yml

@@ -0,0 +1,25 @@
+name: doxygen-github-pages
+
+on:
+  push:
+    branches: master
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Install doxygen
+        run: sudo apt install doxygen graphviz fonts-freefont-ttf
+      - name: Build html docs
+        run: make doxygen && cp -R .circleci docs/html/
+      - name: Deploy gh-pages
+        uses: JamesIves/github-pages-deploy-action@3.5.7
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BRANCH: gh-pages
+          FOLDER: docs/html
+          SINGLE_COMMIT: true