cubicweb-skos #14037638 label's kind and language_code should be indexed [validation pending]

as they are frequently queried

prioritynormal
typebug
done in0.12.1
load left0.000
closed by#f64f72f6ba31 Index Label's kind and language code. Closes #14037638
patchIndex Label's kind and language code. Closes #14037638 [applied]