Upgrade to GitHub-native Dependabot

Author: dependabot-preview[bot]

.github/dependabot.yml

@@ -0,0 +1,15 @@
+version: 2
+updates:
+- package-ecosystem: mix
+  directory: "/"
+  schedule:
+    interval: daily
+    time: "04:00"
+  open-pull-requests-limit: 10
+  ignore:
+  - dependency-name: cors_plug
+    versions:
+    - 2.0.2
+  - dependency-name: plug_cowboy
+    versions:
+    - 2.4.1