Add ToastUI Vue editor to the frontend

Job To Be Done

Add ToastUI 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

• Add @toast-ui/vue-editor dependency.
• Add the necessary test coverage.
• 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 #214559 (closed).

Mockups: #214559 (designs)