Fail DWO startup if it detects another one on the cluster

[sleshchenko]

It's possible that occasionally two DWO are deployed on the cluster, like on with OLM in openshift-operaotors, another in devworkspace-controller with Che or makefile.

And in such a case all DevWorkspace start being reconciled forever.
It's needed that DWO check if it's only one, if not - fail container start up.
It's possible with webhooks which are cluster scoped, then DWO can check if the referenced deployment exists or webhook is just leftover from the previous installation (since OLM don't clean up webhook and webhook server).

[sleshchenko]

On a planning I promised to provide more info about my idea, and what can better explain than code? )
So, https://github.com/devfile/devworkspace-operator/compare/failIfTwoDWOAreDeployed?expand=1
but there is still TODO and maybe there is a better place to do that check.