Changes user password(s) and/or access string.
See https://paws-r.github.io/docs/memorydb/update_user.html for full documentation.
memorydb_update_user(UserName, AuthenticationMode = NULL, AccessString = NULL)[required] The name of the user
Denotes the user's authentication properties, such as whether it requires a password to authenticate.
Access permissions string used for this user.