Reduce dependabot pull requests for web_embedding (#1810)

This configures dependabot to check for out-of-date NPM packages weekly
instead of daily, and limits it to direct dependencies. There could be
more we could do if we dig through the [Configuration options for the
dependabot.yml
file](https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file)
documentation.

cc: @ditman 

fixes #1809

.github/dependabot.yaml

@@ -224,4 +224,6 @@ updates:
   - package-ecosystem: "npm"
     directory: "web_embedding/ng-flutter"
     schedule:
-      interval: "daily"
+      interval: "weekly"
+    allow:
+      - dependency-type: "direct"