Add renovate.json (#12)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/renovate.json5

@@ -0,0 +1,17 @@
+{
+    $schema: "https://docs.renovatebot.com/renovate-schema.json",
+    extends: ["github>HSLdevcom/jore4-tools//renovatebot/jore4-default-preset.json5"],
+
+    // repository-specific additional rules about grouping, exclusions and inclusions
+    // Note: if the rule feels generic enough, should consider adding it to the jore4 default preset
+    packageRules: [
+        {
+            // restrict spring boot updates to <3 versions for now
+            groupName: "spring boot",
+            groupSlug: "spring-boot",
+            matchPackageNames: ["org.springframework.boot"],
+            matchPackagePrefixes: ["org.springframework.boot:"],
+            allowedVersions: "<3",
+        },
+    ],
+}

.github/workflows/check-renovatebot-config.yml

@@ -0,0 +1,17 @@
+name: Check renovatebot config
+
+on:
+  pull_request:
+
+jobs:
+  validate:
+    name: Validate renovatebot config
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Validate
+        uses: suzuki-shunsuke/[email protected]
+        with:
+          config_file_path: .github/renovate.json5