Question: How to use mysqlsh to execute addInstance in silent mode (from a script) and avoid answering such a question?

Please pick an option out of [C]lone/[I]ncremental recover/[A]bort (default Clone):

Adding an instance to InnoDB Cluster requires the specification of what kind of recovery is desired. This can be of two types (incremental or clone), one can be better than another depending on the distance of the data between the candidate instance and the cluster.

As an example, if the instance to be added is empty, the option would be clone. In such a case the command can be executed in silent mode as follows.

cl.addInstance('[USER]@[HOST]:[PORT]', {recoveryMethod: 'clone'})