Adds Firebase resources and enables Firebase services in the specified existing Google Cloud Project. Since a FirebaseProject is actually also a Google Cloud Project, a FirebaseProject has the same underlying Google Cloud identifiers (projectNumber and projectId). This allows for easy interop with Google APIs. The result of this call is an Operation. Poll the Operation to track the provisioning process by calling GetOperation until done is true. When done is true, the Operation has either succeeded or failed. If the Operation succeeded, its response is set to a FirebaseProject; if the Operation failed, its error is set to a google.rpc.Status. The Operation is automatically deleted after completion, so there is no need to call DeleteOperation. This method does not modify any billing account information on the underlying Google Cloud Project. To call AddFirebase, a project member or service account must have the following permissions (the IAM roles of Editor and Owner contain these permissions): firebase.projects.update, resourcemanager.projects.get, serviceusage.services.enable, and serviceusage.services.get.