Fix Cycle Analytics landing widget state and improve state management in Vue.

## What does this MR do?
- Fixes Cycle Analytics help widget show/hide issue
- Addresses initial MR feedback with improving Vue state management logic
- Fixes cookie path of the help widget so when you close a help widget in a repo it won't be visible for other repos.

## Are there points in the code the reviewer needs to double check?
- Should we move `gl.cycleAnalyticsModel` to a new file.

## Why was this MR needed?
- Addresses feedbacks of [initial MR](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5986) and fixes #22483

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [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?
Fixes #22483

See merge request !6492