handle commas in Issue total count

What does this MR do?

strip commas from Issue total when getting text, re-add them when updating

Are there points in the code the reviewer needs to double check?

• toLocaleString will change the content if their locale is different (e.g. for languages that use . as thousand separator
• no comma readded in Safari 9
• maybe we should just use a network request? still have first 2 issues though I guess
• this is still not a great thing...

Why was this MR needed?

Caused by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9216 :(

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added
• [ ] Documentation created/updated
• [ ] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29559 (closed)