[MR Widget] Migrate Status Checks to V2

Context

As part of &10460 (closed), we're migrating existing widgets to V2.

This issue tracks the effort to migrate the Status Checks Widget To V2.

Implementation plan

• Rewrite ee/app/assets/javascripts/vue_merge_request_widget/extensions/status_checks/index.js so that it uses ~/vue_merge_request_widget/components/widget/widget.vue instead of returning a plain object (similar to Migrate terraform widget to V2 (!122209 - merged) • Savas Vedova • 16.2).

Verification steps

• Go to gitlab-org/frontend/playground/gitlab-mr-widgets-demo!26 (closed)
• Check that the Status Check Widget is loading properly
• Check that the Status Check Widget has a pending status and continues to fetch status_checks endpoint