Resolve "Find a way to remove generate_secrets.py from stackspin/stackspin"

Closes #1461 (closed)

• Install secrets controller.
• For all core components that need to generate secrets:
  • Let kustomization depend on the new controller.
  • Add StringSecret and/or BasicAuth manifests to kustomization.
  • Remove calls to old python script from install script.
• For all apps:
  • Let kustomization depend on the new controller.
  • Add StringSecret and/or BasicAuth manifests to kustomization.
  • Remove secret template from dashboard.
• Remove secret generation code from dashboard.
• Remove unused parts of generate_secrets.py.
• Test upgrading an existing cluster to the new setup.