Add argocd plugin

[PatAKnight]

Summary

Brief description of changes in this PR.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• New plugin support (adds integration for a new RHDH plugin)
• Documentation update
• Refactoring (no functional changes)
• CI/CD changes

Related Issues

Closes #(issue number)

Changes Made

• Adds new Argo CD plugin scripts to deploy an Argo CD instance along with some example apps
• Update the plugin scaffolding doc to mention the importance of a round robin approach for plugin deployment

Checklist

General

• I have read the CONTRIBUTING guide
• My code follows the project's code conventions
• I have tested my changes against a real cluster
• If upgrading RHDH version, verified values.yaml is compatible with new chart

Security

• No secrets, tokens, or credentials are included in this PR
• Secret templates contain only placeholders (empty strings or <PLACEHOLDER>)
• No hardcoded cluster URLs or API endpoints

For Plugin Contributions

• Documentation added in docs/<plugin-name>.md
• Configuration script added in scripts/config-<plugin-name>-plugin.sh
• config-plugins.sh updated with new mappings
• Secret templates updated with new placeholders
• Resource manifests added (if required)
• All new scripts are executable (chmod +x)

Testing Notes

Describe how to test these changes:

1. Run ./scripts/config-argocd-plugin.sh against a live OpenShift cluster and verify the ArgoCD operator installed, the ArgoCD instance reached Available status, and the three demo applications (demo-guestbook-app, demo-helm-app, demo-kustomize-app) appear in the ArgoCD UI.
2. Enable each plugin pair independently (Backstage Community, then RoadieHQ) and confirmed the ArgoCD tab appear on the corresponding demo catalog entities in RHDH with correct sync status and health information.
3. Verified the demo catalog entities are discoverable in the RHDH catalog and that annotation-to-application matching work correctly for both argocd/app-name and argocd/app-selector styles.

Screenshots (if applicable)

Add screenshots to help explain your changes.

Todo

Still need to work through testing to ensure that this works as expected