chore(deps): add dependabot config for daily npm updates (#1334)

* chore(deps): add dependabot config for daily npm updates

Configure Dependabot to scan for npm updates daily across the root
workspace and both published packages (docusaurus-plugin-openapi-docs
and docusaurus-theme-openapi-docs).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(deps): simplify dependabot config to root only

Yarn workspaces hoists all dependencies to the root yarn.lock, so
Dependabot only needs to scan from / — it will pick up package.json
files across all workspace packages automatically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sserrata

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: npm
+    directory: /
+    schedule:
+      interval: daily