Add Renovate for dependency management (#130)

.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 +1,31 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "rebaseWhen": "behind-base-branch",
+  "dependencyDashboard": true,
+  "labels": ["dependencies", "no-stale"],
+  "commitMessagePrefix": "⬆️",
+  "commitMessageTopic": "{{depName}}",
+  "regexManagers": [
+    {
+      "fileMatch": ["/Dockerfile$", "/build.yaml$"],
+      "matchStringsStrategy": "any",
+      "matchStrings": [
+        "ARG BUILD_FROM=(?<depName>.*?):(?<currentValue>.*?)\\s+",
+        "(aarch64|amd64|armhf|armv7|i386):\\s[\"']?(?<depName>.*?):(?<currentValue>.*?)[\"']?\\s"
+      ],
+      "datasourceTemplate": "docker"
+    }
+  ],
+  "packageRules": [
+    {
+      "groupName": "Add-on base image",
+      "matchDatasources": ["docker"]
+    },
+    {
+      "groupName": "Add-on base image",
+      "matchDatasources": ["docker"],
+      "matchUpdateTypes": ["patch"],
+      "automerge": true
+    }
+  ]
+}