Format issue list counts

What does this MR do and why?

This MR formats large counts with a thousands separator

Screenshots or screen recordings

before	after

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:vue_issues_list)

2. Visit any group or project issues list page with large counts such as http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.