chore: replace release-please app with GitHub action

Replaces the .github/release-please.yml app configuration with a
release-please-action workflow.

The new workflow in .github/workflows/release-please.yml is equivalent to the old app configuration. It uses a manifest-based release strategy, which is the default for the action when no `release-type` is specified.

Removes comments from the workflow file.

Author: google-labs-jules[bot]

.github/release-please.yml

@@ -0,0 +1,18 @@
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+name: release-please
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: googleapis/release-please-action@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}