Replace use of old term label with attribute (#2790)

* Replace use of old term label with attribute

The specification has unified on the term attribute to describe
key-value pairs. There exist still many hold-overs of the use of the
term label. This updates those uses or deprecates exported types and
functions in favor of renamed forms.

* fix infinite recursion

* Remove backticks from attribute set docs

* Remove LabelFilterSelector entirely

* Remove Metadata.Labels instead of deprecate

* Update changelog with public changes

* Revert OC err msg

sdk/resource/benchmark_test.go

@@ -25,7 +25,7 @@ import (
 
 const conflict = 0.5
 
-func makeLabels(n int) (_, _ *resource.Resource) {
+func makeAttrs(n int) (_, _ *resource.Resource) {
 	used := map[string]bool{}
 	l1 := make([]attribute.KeyValue, n)
 	l2 := make([]attribute.KeyValue, n)
@@ -51,7 +51,7 @@ func makeLabels(n int) (_, _ *resource.Resource) {
 }
 
 func benchmarkMergeResource(b *testing.B, size int) {
-	r1, r2 := makeLabels(size)
+	r1, r2 := makeAttrs(size)
 
 	b.ReportAllocs()
 	b.ResetTimer()

sdk/resource/resource.go

@@ -194,7 +194,7 @@ func Merge(a, b *Resource) (*Resource, error) {
 	mi := attribute.NewMergeIterator(b.Set(), a.Set())
 	combine := make([]attribute.KeyValue, 0, a.Len()+b.Len())
 	for mi.Next() {
-		combine = append(combine, mi.Label())
+		combine = append(combine, mi.Attribute())
 	}
 	merged := NewWithAttributes(schemaURL, combine...)
 	return merged, nil