Add CI/CD Guide for Harness

[meagancojocar]

Problem

We lack a dedicated CI/CD guide for using Harness with Pulumi. While we cover many popular systems under /docs/iac/using-pulumi/continuous-delivery/ (e.g., GitHub Actions, GitLab CI, CircleCI), Harness is missing—despite growing adoption and strong infrastructure deployment capabilities.

Affected Area

Documentation – CI/CD guides section.

Proposed Solution

Create a new guide at /docs/iac/using-pulumi/continuous-delivery/harness.md with:

• Overview of Harness and its integration with Pulumi
• Prerequisites
• Step-by-step configuration
• Example pipeline YAMLs deploying Pulumi stacks
• Best practices (e.g., approvals, canary deployments, rollbacks)
• Troubleshooting tips