[RN] When starting a workspace with the same name as an existing one ask users if they wants to replace the pre-existing one

= Improved UX of starting new workspaces with name conflicts Before this update, starting a workspace with a name that was in use for another workspace resulted in the *Creating a workspace* page showing a *Failed to create a workspace* error message. With this update, the *Creating a workspace* page warns users of an *Existing workspace found* and prompts users to *Open the existing workspace* or *Create a new workspace*.