Add tabs override variable to ocp4_workload_showroom

[prakhar1985]

Summary

• Adds ocp4_workload_showroom_tabs variable (default: [])
• Passes tab config as JSON to the deployer Helm chart via content.tabs
• Allows overriding ui-config.yml tabs at deploy time from AgnosticV catalog

Related PRs

• showroom-deployer: Add SHOWROOM_TABS env var for runtime tab override rhpds/showroom-deployer#49 (Helm env var passthrough)
• showroom-images: rhpds/showroom-images#37 (entrypoint configure_tabs() function)

Example usage in AgnosticV

ocp4_workload_showroom_tabs:
  - name: OCP Console
    url: "https://console-openshift-console.apps.{{ guid }}.{{ sandbox_domain }}"
  - name: ArgoCD
    url: "https://openshift-gitops-server-openshift-gitops.apps.{{ guid }}.{{ sandbox_domain }}"

Empty list (default) preserves the content repo's ui-config.yml tabs.