ci: adds new github workflow focused on documentation in prep to deprecate kokoro presubmit

.github/workflows/docs.yml

@@ -0,0 +1,39 @@
+on:
+  pull_request:
+    branches:
+      - main
+name: docs
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.10'
+    - name: Install nox
+      run: |
+        python -m pip install --upgrade setuptools pip wheel
+        python -m pip install nox
+    - name: Run docs session
+      run: |
+        nox -s docs-3.10
+
+  docfx:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.10'
+    - name: Install nox
+      run: |
+        python -m pip install --upgrade setuptools pip wheel
+        python -m pip install nox
+    - name: Run docsfx session
+      run: |
+        nox -s docsfx-3.10