Replying it for community:I found the way The exact path which need to
overlay for this is /libs/granite/ui/content/shell/header/actions and we
can add our extra icon and then we can use clientlib js to perform any
act ion if required Please note : Still not sure it is recommeded that
we should overlay these nodes or do customisation as in aem it is not
allowing to overlay .You can copy and paste the node and do the
customisation still.