Added Drupal styles workflow

Author: rimi-itk

github/workflows/drupal/styles.yaml

@@ -0,0 +1,36 @@
+# Do not edit this file! Make a pull request on changing
+# github/workflows/styles.yaml in
+# https://github.com/itk-dev/devops_itkdev-docker if need be.
+
+### Styles (CSS and SCSS)
+###
+### Validates styles files.
+###
+### #### Assumptions
+###
+### 1. A docker compose service named `prettier` for running
+###    [Prettier](https://prettier.io/) exists.
+
+name: Styles
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+      - develop
+
+jobs:
+  styles-lint:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - run: |
+          docker network create frontend
+
+      - run: |
+          docker compose run --rm prettier 'web/themes/custom/**/css/**/*.css' --check