Allows to change a Live Data configuration programmatically from a Javascript API

Currently the only way to customize a livedata configuration is to provide a json configuration in the body of the macro (or of course, to use the UI's configuration panels).
It is interesting to also be possible to update this configuration programmatically using a Javascript API, for instance to add a new column to the Live Data.

This is for instance useful for XWIKI-18753 where user profile columns can be added to the table when the customization options are changed.