Move mr widget related links into a vue file

What does this MR do?

1. Moves mr_widget_related_links into a vue file
2. Adds i18n
3. Moves some logic out of the component

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

I removes the check for related links in here https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/new/diffs?merge_request%5Bsource_branch%5D=fl-mr-widget#c62746b2e7692f2d7b0f8c6879b77d83e49cde82_24_28 since it's already done when we assign it https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js#L38 and check for it again here https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/vue_merge_request_widget/mr_widget_options.js#L258

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug (changed)
• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/41582 https://gitlab.com/gitlab-org/gitlab-ce/issues/34371