fix(explorer): `metric` facet strategy not available with multiple columns
fix(explorer): `metric` facet strategy not available with multiple columns

OurWorldInData/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,owid/owid-grapher