Add CI/CD guide for ArgoCD

[meagancojocar]

Problem

Our CI/CD documentation lacks a dedicated guide for using ArgoCD with Pulumi. While ArgoCD is mentioned in the Kubernetes Operator docs and a few blog posts, it deserves a standalone guide—similar to existing ones for GitHub Actions, GitLab CI, CircleCI, etc.—under /docs/iac/using-pulumi/continuous-delivery/.

Affected Area

Documentation – CI/CD guides section.

Proposed Solution

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

• Overview of ArgoCD and its role in GitOps with Pulumi
• Prerequisites for integration
• Step-by-step configuration
• Example ArgoCD Application YAMLs deploying Pulumi stacks
• GitOps best practices
• Troubleshooting tips