Missing unit label in NumberList directive

[maryia-lapata]

unitName is not displayed on a panel:

https://github.com/elastic/kibana/blob/master/src/ui/public/number_list/number_list.html#L43

That's because getUnitName uses an attribute unit while this directive is invoked with attribute unitName.

[elasticmachine]

Pinging @elastic/kibana-app

[maryia-lapata]

This issue was fixed in #35349.