Add a new TechPreviewNoUpgrade feature gate for the Own/SingleNamespace InstallMode feature.

See dev guide for more information: https://docs.google.com/document/d/1krN-4vwaE47aLRW9QjwD374-0Sh80taa_7goqVNi_-s/edit?tab=t.0#heading=h.tm6pdgnj5tj 

AC:

• openshift/api PR for adding a new feature gate with name NewOLMOwnSingleNamespace