Add helm chart documentation for workspaces

Summary

Add documentation for enabling workspaces through GitLab Chart.

Related : #6186 (comment 2853995465)

Steps to reproduce

N.A.

Configuration used

N.A.

Current behavior

Docs for enabling/configuring workspaces is missing.

Expected behavior

Docs for enabling/configuring workspaces must be available.

Versions

• Chart: (tagged version | branch | hash git rev-parse HEAD)
• Platform:
  • Cloud: (GKE | AKS | EKS | ?)
  • Self-hosted: (OpenShift | Minikube | Rancher RKE | ?)
• Kubernetes: (kubectl version)
  • Client:
  • Server:
• Helm: (helm version)
  • Client:
  • Server:

Relevant logs

(Please provide any relevant log snippets you have collected, using code blocks (```) to format)