Creates an instance configuration and begins preparing it to be used. The returned long-running operation can be used to track the progress of preparing the new instance configuration. The instance configuration name is assigned by the caller. If the named instance configuration already exists, CreateInstanceConfig returns ALREADY_EXISTS. Immediately after the request returns: * The instance configuration is readable via the API, with all requested attributes. The instance configuration's reconciling field is set to true. Its state is CREATING. While the operation is pending: * Cancelling the operation renders the instance configuration immediately unreadable via the API. * Except for deleting the creating resource, all other attempts to modify the instance configuration are rejected. Upon completion of the returned operation: * Instances can be created using the instance configuration. * The instance configuration's reconciling field becomes false. Its state becomes READY. The returned long-running operation will have a name of the format /operations/ and can be used to track creation of the instance configuration. The metadata field type is CreateInstanceConfigMetadata. The response field type is InstanceConfig, if successful. Authorization requires spanner.instanceConfigs.create permission on the resource parent.