Documentation: Offline installation

Fix #1056 (closed) #1055 (closed) #1054 (closed)

• Better docs for offline installation
• Fixed docs CI/CD warnings.
• Offline installation script changes:
  • offline mode is not inferred when chart-path is present
  • offline mode requires chart-path
  • Dev mode set to false is not inferred in offline mode
  • Pull Policy: IfNotPresent is set in offline mode
• offline_install_gpu.py and gpu_operator.tgz are copied (during offline build) to the build directory, so deploy script can access them