[CI] set_indices ros service (suggestion)

[IoannisDadiotis]

This is a suggestion for enhancing the ROS API of Cartesian Interface. @alaurenzi

I came across a situation where I need to change the indices of a cartesian task on the fly, i.e. without manually editing the stack of tasks and restarting cartesian interface, in order to examine the behavior of my WBC. Despite the many services available (*/set_active, */set_base_link, */set_lambda, */set_weight), this functionality is currently not available, if I am not wrong.

I think it would be useful to provide a */set_indices service to implement this.