feat: Host rustdoc of master on GitHub pages (#3126)

This PR hosts the documentation of the current master branch on GitHub Pages. The URL should be: https://libp2p.github.io/rust-libp2p

Author: umgefahren

.github/workflows/docs.yml

@@ -0,0 +1,48 @@
+name: Build and host documentation
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    name: Build documentation
+    runs-on: ubuntu-latest
+    steps:
+    - name: Install Protoc
+      uses: arduino/setup-protoc@v1
+    - name: Checkout 
+      uses: actions/checkout@v3
+    - name: Install nightly toolchain
+      run: rustup toolchain install nightly 
+    - name: Build Documentation
+      run: cargo +nightly doc --no-deps --workspace -F full
+      env:
+        RUSTDOCFLAGS: "--cfg docsrs"
+        RUSTFLAGS: "--cfg docsrs"
+    - name: Add index file
+      run: |
+        mkdir host-docs
+        echo "<meta http-equiv=\"refresh\" content=\"0; url=libp2p\">" > target/doc/index.html
+        cp -r target/doc/* ./host-docs
+    - name: Upload documentation
+      uses: actions/upload-pages-artifact@v1.0.4
+      with:
+        path: "host-docs/"
+
+  deploy:
+    name: Deploy documentation
+    needs: build
+    permissions:
+      pages: write
+      id-token: write
+
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v1
+