Add copilot-setup-steps.yml to configure agent environment

Agent-Logs-Url: https://github.com/bramp/ffmpeg-cli-wrapper/sessions/ad7a0e4c-5c9d-4345-bd38-ddd420848ae8

Co-authored-by: bramp <160627+bramp@users.noreply.github.com>

Author: Copilot

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

@@ -0,0 +1,43 @@
+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-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+          cache: maven
+
+      # Pre-download all Maven dependencies (including from central.sonatype.com and
+      # checkstyle.org) during setup, which is exempt from the agent's firewall.
+      # This ensures the agent can build, test, and lint without needing network access
+      # to those hosts at runtime.
+      - name: Pre-download Maven dependencies
+        run: mvn --batch-mode dependency:go-offline -Dgpg.skip
+
+      - name: Pre-download Maven plugin dependencies
+        run: mvn --batch-mode fmt:check checkstyle:check --fail-never -Dgpg.skip