Add ToastUI Vue editor to the frontend
## Job To Be Done
Add [ToastUI Vue editor](https://github.com/nhn/tui.editor/tree/master/apps/vue-editor) to the frontend and wrap the 3rd party component.
## Behaviour
- This should have no impact on the current behavior of the SSE.
- No visual changes to our SSE are expected.
- All test coverage for the component wrapper should be added as part of this iteration.
## Tasks
* [x] Add @toast-ui/vue-editor dependency.
* [x] Add the necessary test coverage.
* [x] Wrap ToastUI editor in a Vue component (outside of the SSE directory).
## Epic & Design mockups
This issue is part of delivering the feature described in https://gitlab.com/gitlab-org/gitlab/-/issues/214559.
Mockups: https://gitlab.com/gitlab-org/gitlab/-/issues/214559/designs
issue