all: switch from Dependabot to Renovate

.github/dependabot.yml

@@ -1,6 +0,0 @@
-version: 2
-updates:
-  - package-ecosystem: "cargo"
-    directory: "/"
-    schedule:
-      interval: "weekly"

renovate.json

@@ -0,0 +1,12 @@
+{
+  "extends": [
+    "config:base"
+  ],
+  "packageRules": [
+    {
+      "matchPackagePatterns": ["*"],
+      "automerge": true,
+      "automergeType": "branch"
+    }
+  ]
+}