Disallow updating experiment with the 'default' conditionCode in frontend

Currently, the backend doesn't allow using 'default' as a conditionCode in an experiment. Therefore we should not allow this in the frontend before a request is made for better user experience.

In the Add/Edit Condition modal, typing 'default' into Condition field should be invalid showing an alert message saying that it is not allowed, and the "Create" or "Save" button should be disabled.