[single-host] none existing URLs to workspace should respond with 404

[sleshchenko]

Describe the bug

[single-host] none existing URLs to workspace should respond with 404.

It's inspired by the issue #19931 (CRW link can be found there as well), so technically, Dashboard remembered the previous run URL and tried to load it, so instead of getting 404, frame was redirected to Che API which redirected to dashboard so we ended with double dashboard.
If some plugin did mistake and used wrong URL, they will get Dashboard as well, instead of 404.

So, I expect gateway in addition to rules for server, add one common for all the workspaces, like /server*, which will just return 404.

Che version

• latest
• nightly
• other: please specify

Steps to reproduce

1. Deploy Che in Single host.
2. Try to open URL for non-existing workspace server, like CHE_HOST/serverany-non-existing.

Expected behavior

404 is returned.

Runtime

• kubernetes (include output of kubectl version)
• Openshift (include output of oc version)
• minikube (include output of minikube version and kubectl version)
• minishift (include output of minishift version and oc version)
• docker-desktop + K8S (include output of docker version and kubectl version)
• other: (please specify)

Screenshots

Installation method

• chectl
  • provide a full command that was used to deploy Eclipse Che (including the output)
  • provide an output of chectl version command
• OperatorHub
• I don't know

Environment

• my computer
  • Windows
  • Linux
  • macOS
• Cloud
  • Amazon
  • Azure
  • GCE
  • other (please specify)
• Dev Sandbox (workspaces.openshift.com)
• other: please specify

Eclipse Che Logs

Additional context