Add release-plz for automated releases

We already use this tool for `libc`, `libm`, and `compiler-builtins` so
anyone with write access can publish releases. Add the required workflow
here.

.github/workflows/publish.yml

@@ -0,0 +1,27 @@
+name: Release-plz
+
+permissions:
+  pull-requests: write
+  contents: write
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  release-plz:
+    name: Release-plz
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Install Rust (rustup)
+        run: rustup update nightly --no-self-update && rustup default nightly
+      - name: Run release-plz
+        uses: MarcoIeni/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}