Add Dependabot configuration and dependency submission workflow

[Shashankpgit]

Summary

• Enables Dependabot to automatically open weekly PRs for outdated npm dependencies across all three workspaces (root, projects/sunbird-video-player, web-component) and keeps
  GitHub Actions versions current.
• Adds a dependency-submission workflow to populate the GitHub Dependency Graph, which Dependabot uses to detect transitive vulnerabilities.
• Schedules dependency submission at 03:00 UTC (Monday) so the graph is fresh before Dependabot runs at 03:30.

Changes

• Add .github/dependabot.yml — four Dependabot update blocks: npm root (with groups for Angular, Sunbird, Karma/Jasmine, and @types/), npm library, npm web-component, and
  github-actions
• Add .github/workflows/dependency-submission.yml — three parallel jobs that submit the dependency graph for each npm workspace; triggers on push/PR to master (when lock files
  change), weekly schedule, and workflow_dispatch

How to Test

1. Merge this PR into master.
2. Navigate to Settings → Code security → Dependency graph on GitHub — all three npm sub-projects should appear as registered manifests within a few minutes.
3. Navigate to Insights → Dependency graph and confirm packages from package-lock.json, projects/sunbird-video-player/package-lock.json, and the generated
   web-component/package-lock.json are listed.
4. On the following Monday (or trigger Actions → Dependency Submission → Run workflow manually), verify the workflow completes successfully.
5. By 03:30 UTC the next Monday, Dependabot should open its first batch of update PRs labelled dependencies.

Checklist

• Tests added or updated
• Documentation updated (if public API or behavior changed)
• No breaking changes — or breaking changes noted with ! in title and explained in Summary
• Reviewed my own diff before requesting review