ci: add Dependabot config for github-actions and swift

Adds weekly Dependabot updates for both ecosystems used by the repo:
GitHub Actions (the main supply-chain surface — workflows currently
have unpinned dependencies that should drift forward over time) and
SwiftPM (currently just swift-openapi-runtime, but worth tracking).

Open PR limit of 5 per ecosystem keeps things manageable, and the
commit prefixes (`ci` / `deps`) sort cleanly in changelogs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: Krivoblotsky

.github/dependabot.yml

@@ -0,0 +1,23 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 5
+    commit-message:
+      prefix: "ci"
+    labels:
+      - "dependencies"
+      - "github-actions"
+
+  - package-ecosystem: "swift"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 5
+    commit-message:
+      prefix: "deps"
+    labels:
+      - "dependencies"
+      - "swift"