cubicweb-timeseries #2556458 relax format_preferences cardinality [validation pending]

the 11 is quite annoying in some cases
let it be ?1

prioritynormal
typeenhancement
done in1.4.0
load0.100
load left0.000
closed by#5ccc169eeec5 [schema] relax format_preferences cardinality (closes #2556458)
patch[schema] relax format_preferences cardinality (closes #2556458) [applied]