Migrate all workflows to GitHub Actions

This commit completes the migration from Concourse to GitHub Actions,
adding the CI variants and release workflows.

See gh-1024

.github/workflows/ci.yml

@@ -0,0 +1,41 @@
+name: CI
+on:
+  push:
+    branches:
+      - main
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+jobs:
+  ci:
+    name: '${{ matrix.os.name}} | Java ${{ matrix.java.version}}'
+    runs-on: ${{ matrix.os.id }}
+    if: ${{ github.repository == 'spring-projects/spring-graphql' }}
+    strategy:
+      matrix:
+        os:
+          - id: ubuntu-latest
+            name: Linux
+        java:
+          - version: 21
+            toolchain: true
+          - version: 22
+            toolchain: true
+    steps:
+      - name: Check Out Code
+        uses: actions/checkout@v4
+      - name: Build
+        id: build
+        uses: ./.github/actions/build-and-publish
+        with:
+          java-version: ${{ matrix.java.version }}
+          java-distribution: ${{ matrix.java.distribution || 'liberica' }}
+          java-toolchain: ${{ matrix.java.toolchain }}
+          develocity-access-key: ${{ secrets.GRADLE_ENTERPRISE_SECRET_ACCESS_KEY }}
+      - name: Send Notification
+        uses: ./.github/actions/send-notification
+        if: always()
+        with:
+          webhook-url: ${{ secrets.GOOGLE_CHAT_WEBHOOK_URL }}
+          status: ${{ job.status }}
+          build-scan-url: ${{ steps.build.outputs.build-scan-url }}
+          run-name: ${{ format('{0} | {1} | Java {2}', github.ref_name, matrix.os.name, matrix.java.version) }}