Add instrumentation scope attributes (#3131)

* Add WithScopeAttributes TracerOption to trace API

* Add Attributes field to instrumentation Scope

* Use scope attributes for new Tracer

* Fix stdouttrace expected test output

* Allow unexported Set fields in sdk/trace test

* Export instrumentation scope attrs in OTLP

* Add changes to the changelog

* Fix imports with make lint

* Add unit tests for WithScopeAttributes

* Fix English in Scope documentation

sdk/trace/trace_test.go

@@ -911,6 +911,8 @@ func TestSetSpanStatusWithoutMessageWhenStatusIsNotError(t *testing.T) {
 func cmpDiff(x, y interface{}) string {
 	return cmp.Diff(x, y,
 		cmp.AllowUnexported(snapshot{}),
+		cmp.AllowUnexported(attribute.Set{}),
+		cmp.AllowUnexported(attribute.Distinct{}),
 		cmp.AllowUnexported(attribute.Value{}),
 		cmp.AllowUnexported(Event{}),
 		cmp.AllowUnexported(trace.TraceState{}))