Add Renovate configuration for automated dependency updates

Configures Renovate with the same patterns used in liquid-ceph:
- Groups minor/patch external deps into a single PR
- Automerges github.com/sapcc and github.com/cobaltcore-dev deps
- Gates Go minor/major version bumps behind dashboard approval
- Runs go mod tidy after updates
- Schedules PRs for Friday mornings
- Enables OSV vulnerability alerts

Author: senolcolak

.github/renovate.json

@@ -0,0 +1,71 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended",
+    "default:pinDigestsDisabled",
+    "mergeConfidence:all-badges",
+    "docker:disable"
+  ],
+  "commitMessageAction": "Renovate: Update",
+  "constraints": {
+    "go": "1.26"
+  },
+  "dependencyDashboardOSVVulnerabilitySummary": "all",
+  "osvVulnerabilityAlerts": true,
+  "postUpdateOptions": [
+    "gomodTidy",
+    "gomodUpdateImportPaths"
+  ],
+  "packageRules": [
+    {
+      "matchPackageNames": [
+        "/.*/"
+      ],
+      "matchUpdateTypes": [
+        "minor",
+        "patch"
+      ],
+      "groupName": "External dependencies"
+    },
+    {
+      "matchPackageNames": [
+        "/^github\\.com\\/sapcc\\/.*/"
+      ],
+      "automerge": true,
+      "groupName": "github.com/sapcc"
+    },
+    {
+      "matchPackageNames": [
+        "/^github\\.com\\/cobaltcore-dev\\/.*/"
+      ],
+      "automerge": true,
+      "groupName": "github.com/cobaltcore-dev"
+    },
+    {
+      "matchPackageNames": [
+        "go",
+        "golang",
+        "actions/go-versions"
+      ],
+      "groupName": "golang",
+      "separateMinorPatch": true
+    },
+    {
+      "matchPackageNames": [
+        "go",
+        "golang",
+        "actions/go-versions"
+      ],
+      "matchUpdateTypes": [
+        "minor",
+        "major"
+      ],
+      "dependencyDashboardApproval": true
+    }
+  ],
+  "prHourlyLimit": 0,
+  "schedule": [
+    "before 8am on Friday"
+  ],
+  "semanticCommits": "disabled"
+}