Add repository analytics storybook stories

What does this MR do and why?

Adds basic storybook stories for the repository analytics components

• test_coverage_summary.vue
• test_coverage_table.vue

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Follow the steps to run storybook locally.
2. When storybook has launched, navigate to EE > Analytics > Repository analytics to see the stories

Related to #428288 (closed)