Replace jQuery.timeago with timeago.js

## What does this MR do?
Replaces jQuery.timeago with [timeago.js](https://github.com/hustcc/timeago.js)

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

*  Check to make sure its working everywhere 😄 
*  Check to make sure the timeago wording matches what we have now (I think I've got this down but an extra pair of 👀 would help too)

## Why was this MR needed?

*  The jQuery.timeago version we have is outdated
*  timeago.js is smaller (7.19 KB => 4.52 KB)
* timeago.js has no jQuery dependency
* removes all inline javascript ⚔  for timeago

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #21793

See merge request !6274