Upgrade to GitHub-native Dependabot

.github/dependabot.yml

@@ -0,0 +1,18 @@
+version: 2
+updates:
+- package-ecosystem: cargo
+  directory: "/"
+  schedule:
+    interval: monthly
+    time: "04:00"
+    timezone: Europe/Berlin
+  ignore:
+  - dependency-name: indicatif
+    versions:
+    - "< 0.11, >= 0.10.a"
+  - dependency-name: rand
+    versions:
+    - 0.8.3
+  - dependency-name: serde
+    versions:
+    - 1.0.123