chore: add weekly Dependabot checks for npm and GitHub Actions

Configure Dependabot to open weekly PRs for npm dependency updates
and GitHub Actions version bumps, with @scope3data/platform as reviewer.

Author: benminer

.github/dependabot.yml

@@ -0,0 +1,15 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    reviewers:
+      - "scope3data/platform"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    reviewers:
+      - "scope3data/platform"