feat: Define edge types and create React Flow edge components

[lornakelly]

Description

Create react flow edge types and the node components associated with them ( Custom Edges ).

Motivation

Edges carry meaning in a workflow diagram - a user needs to be able to distinguish at a glance between a normal sequential transition, a conditional branch, and an error path. Defining the edge types now ensures that meaning is captured correctly in the diagram from the start.

Proposed Implementation

• Create a directory named "edges" under "react-flow" to host edge custom components specifics. The following three edge types are required:
  • Default/regular - simple line, used for sequential flow between tasks
  • conditional - line with a condition label, used for switch branches
  • error - solid red line, used for error transitions
• Update the hardcoded diagram to showcase all edge types.

Definition of Done

• Implementation: Fully implemented according to the Serverless Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.