chore: adds dependabot.yml (#595)

* chore: adds dependabot.yml

* update based on orbitsdk learning

* simplify

* only internal deps

---------

Co-authored-by: Fionna Chan <13184582+fionnachan@users.noreply.github.com>

Author: douglance

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+  - package-ecosystem: npm
+    directories:
+      - '**/*'
+    schedule:
+      interval: daily
+    versioning-strategy: increase
+    open-pull-requests-limit: 5
+    allow:
+      - dependency-name: '@arbitrum/*'
+      - dependency-name: '@offchainlabs/*'