feat: create copilot-setup-steps.yml (#4794)

* feat: create `copilot-setup-steps.yml`

As suggested within https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment#preinstalling-tools-or-dependencies-in-copilots-environment we'd like to ensure that Copilot starts with a correct environment and w/o the need to determine it's setup itself.

* Update copilot-setup-steps.yml

---------

Co-authored-by: Michael Kraus <michael.m.kraus@deutschebahn.com>

Author: mfranzke

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,40 @@
+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-24.04 # Use Ubuntu 24.04 explicitly
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # If you want to clone the repository as part of your setup steps, for example to install dependencies, you'll need the `contents: read` permission. If you don't clone the repository in your setup steps, Copilot will do this for you automatically after the steps complete.
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v5
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: ".nvmrc"
+          cache: "npm"
+
+      - name: Install JavaScript dependencies
+        run: npm ci
+
+# TODO: we probably would want to enhance this with further aspects like e.g. linting or testing. But we would need to determine the tradeoff in between slowing down Copilot with this, as we would most likely run some of this work later on within the PR anyhow.