Add LLM Usage Guidance to CONTRIBUTING.md

[lornakelly]

Description

Add a section to CONTRIBUTING.md outlining guidelines for using Large Language Models (LLMs) when contributing to this repository, aligned with the approach used in Quarkus.

Motivation

LLM tools are increasingly used when contributing code. Without clear guidance, this can lead to inconsistent quality and changes that aren’t fully understood by contributors.

Adding guidance to CONTRIBUTING.md helps set clear expectations that all code must be reviewed, understood, and meet project standards, regardless of how it was created. This keeps the quality bar high and makes reviews smoother as the project grows.

Proposed Implementation

No response

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.