[codex] add release please workflow

.github/workflows/release-please.yaml

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+name: Release Please
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Release Please
+        id: release
+        uses: googleapis/release-please-action@16a9c90856f42705d54a6fda1823352bdc62cf38
+        with:
+          token: ${{ secrets.RELEASE_PLEASE_TOKEN || github.token }}
+          command: manifest
+          config-file: release-please-config.json
+          manifest-file: .release-please-manifest.json

.release-please-manifest.json

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+{
+  ".": "0.0.0"
+}

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.

release-please-config.json

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+{
+  "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
+  "packages": {
+    ".": {
+      "release-type": "node",
+      "changelog-path": "CHANGELOG.md"
+    }
+  }
+}