Migrate doc from RTD to gh-pages (#2460)

* gh-pages workflow

* update doc.yml

* update

* remove RTD

* change action to main

* test fail on warning

* fail on warnings

* get back .readthedocs.yml, a bit cleanup

* revert SHA of index.md file

.github/workflows/doc.yml

@@ -0,0 +1,33 @@
+name: Docs
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: write
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v3
+        with:
+          python-version: '3.9'
+      - name: Install dependencies
+        run: |
+          pip install .[docs]
+      - name: Sphinx build
+        # fail on warnings
+        run: |
+          sphinx-build docs _build -W --keep-going
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          publish_branch: gh-pages
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: _build/
+          force_orphan: true
+        #   cname: docs.nerf.studio