Bootstrap merge request reports tab Vue app

https://gitlab.com/gitlab-org/gitlab/-/issues/462123/designs/MR_-_Reports_tab_-_Violations_-_Default.png

• New tab in the merge request tab bar
  • Remember the sticky header here as that has its own component
• New Rails route to handle the linking to the tab
  • We can copy what exists for overview/pipeline/diffs/commits
• Vue router to allow for linking between the different reports in the tab