Add GitHub Actions workflow for updating CONTRIBUTORS.md

- Implemented a new GitHub Actions workflow named 'update-contributors' to automate the process of updating the CONTRIBUTORS.md file.
- Set up the workflow to run daily at 2am UTC and on demand via workflow_dispatch.
- Added steps to checkout the repository, install jq, update the CONTRIBUTORS.md file with contributors' GitHub usernames, and create a pull request.

Signed-off-by: urasakikeisuke <[email protected]>

.github/workflows/update-contributors.yaml

@@ -0,0 +1,45 @@
+name: Update CONTRIBUTORS.md
+
+on:
+  schedule:
+    - cron: '0 2 * * *' # Runs every day at 2am UTC
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - name: Setup jq
+      uses: dcarbone/install-jq-action@v2
+
+    - name: Update CONTRIBUTORS.md
+      run: |
+        echo "# Contributors" > CONTRIBUTORS.md
+        p=1
+        while true; do
+          s=$(curl "https://api.github.com/repos/mapiv/pypcd4/contributors?page=$p") || break
+          [ "0" = $(echo $s | jq length) ] && break
+          echo $s | jq -r '.[] | "* " + .login + ""'
+          p=$((p+1))
+        done | sort -f | tee -a CONTRIBUTORS.md
+
+    - name: Create Pull Request
+      uses: peter-evans/create-pull-request@v6
+      with:
+        token: ${{ secrets.GITHUB_TOKEN }}
+        commit-message: Update CONTRIBUTORS.md
+        title: Update CONTRIBUTORS.md
+        body: |
+          This PR updates the list of contributors in CONTRIBUTORS.md.
+          This PR is automatically generated by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub Actions.
+        branch: update-contributors
+        add-paths: |
+          CONTRIBUTORS.md
+        labels: |
+          rd/chore