[release-0.16] 🏃 Make client.MatchingLabels faster

[timflannagan]

Carries the upstream commit that fixes the client.MatchingLabels performance regression we were seeing in various product codebases. This also picks up another upstream commit that has landed in the release-0.16 branch since this branch was last created:

$ git diff upstream/release-0.16
diff --git a/pkg/client/options.go b/pkg/client/options.go
index d81bf25d..ee6489b7 100644
--- a/pkg/client/options.go
+++ b/pkg/client/options.go
@@ -514,7 +514,8 @@ type MatchingLabels map[string]string
 func (m MatchingLabels) ApplyToList(opts *ListOptions) {
        // TODO(directxman12): can we avoid reserializing this over and over?
        if opts.LabelSelector == nil {
-               opts.LabelSelector = labels.NewSelector()
+               opts.LabelSelector = labels.SelectorFromValidatedSet(map[string]string(m))
+               return
        }
        // If there's already a selector, we need to AND the two together.
        noValidSel := labels.SelectorFromValidatedSet(map[string]string(m))

Now, the only differences between the upstream and downstream release-0.16 branches are we picked up a commit that hasn't been backported.