[feature] Add sticky notes in the workflow editor

**As a** Workflow developer

**I want to** add sticky notes to my workflow editor while building a workflow

**So that** I can document parts of my workflow

Technical Details
- Notes should support writing in the Markdown format
- Notes should support embedding YouTube videos
- Notes should allow for the color change(default is yellow)

Acceptance Criteria
TODO

Definition of Done
TODO

Start by locating the workflow editor entry point and reviewing how workflow elements are represented and persisted. Define the scope for Markdown, YouTube embedding, and color selection before implementation, since the acceptance criteria and definition of done are currently TODO.

Written by the indexing model from the issue text.