[MR Widget] Migrate Metrics Widget to V2

Context

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

This issue tracks the effort to migrate the Metrics Widget To V2.

Implementation plan

• Rewrite ee/app/assets/javascripts/vue_merge_request_widget/extensions/metrics/index.js so that it uses ~/vue_merge_request_widget/components/widget/widget.vue instead of returning a plain object.
• Make sure to set pipeline:run-all-e2e to capture failing E2E tests when the MR is ready

Example MR

Migrate Status Checks to V2 (!125668 - merged) • Savas Vedova • 16.3