Rewrite mockQuerier to be able to return histograms

[krajorama]

Rewrite mockQuerier to be initialized with implicit native histograms to be able to serve them during Select

mimir/pkg/querier/remote_read_test.go

Line 45 in 651a8ed

type mockQuerier struct {

[leizor]

I think I've got this in one of my branches already--I'll dig it up.

IIRC the way I did it also removes a dependency on series.MatrixToSeriesSet; I'll see if we also can't address #4378 here. Oops got my wires crossed--that issue isn't talking about the same function.

[krajorama]

done in #4425

[krajorama]

also partly done in #4444