Add Renovate for dependency management (#80)

.github/dependabot.yaml

@@ -1,8 +0,0 @@
----
-version: 2
-updates:
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: daily
-      time: "06:00"

.github/renovate.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "rebaseWhen": "behind-base-branch",
+  "dependencyDashboard": true,
+  "labels": ["dependencies", "no-stale"],
+  "commitMessagePrefix": "⬆️",
+  "commitMessageTopic": "{{depName}}",
+  "packageRules": [
+    {
+      "matchManagers": ["github-actions"],
+      "addLabels": ["github_actions"],
+      "rangeStrategy": "pin"
+    },
+    {
+      "matchManagers": ["github-actions"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "automerge": true
+    }
+  ]
+}