Update task_list to version 2.0.0

What does this MR do?

• Updates the task_list library to 2.0.0
  • Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/22470, task lists in code blocks
  • Uses a vanilla js core, so jQuery can be dropped at will
  • Removes some pinned gems that were only needed for old versions of ruby
• Manages the javascript asset of task_list using yarn
• Removes the manually patched vendor script for task_list

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

It might be necessary to perform a security review of both the gem contents and the npm package since they are not in the diff.

• https://github.com/deckar01/task_list/compare/1.0.6...v2.0.0
• https://rubygems.org/gems/deckar01-task_list
• https://www.npmjs.com/package/deckar01-task_list

Why was this MR needed?

we have a patched version of your library and it will be pain in the ass if we want to update it later.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6837#note_16967841

task_list.js was tracked as a vendor script that had to be patched manually. This new version is published to npm and avoids the need for manual updated by making jQuery optional.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
• 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 #22470 (closed)