Don't allow to start workspace if user already reached runtime number limit

[maxandersen]

Is your enhancement related to a problem? Please describe.

when I create a second workspace on che.openshift.io it only errors after changing screens, loaded a bit and then it errors that I have already one workspace open.

Describe the solution you'd like

On the create workspace screen where the UI already knows I have 1 workspace running, block or at least warn me from creating a workspace if my limit only allows for 1 workspace.

The current mechanism is very tedious to work with.

[che-bot]

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