Add missing apply_to_spans section support (#2301)

This bug was uncovered during spec review here:
https://github.com/open-telemetry/opentelemetry-specification/pull/2008#discussion_r731359448

apply_to_spans section was missing although it is implied to
be present in the description of how span changes section
is supposed to work.

This fixes the omission by adding apply_to_spans section.
This is not a new feature, just fixing a bug in file format description
and in the corresponding implementation.

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

schema/v1.0/ast/spans.go

@@ -30,7 +30,14 @@ type SpanEvents struct {
 
 // SpansChange corresponds to a section representing spans change.
 type SpansChange struct {
-	RenameAttributes *RenameAttributes `yaml:"rename_attributes"`
+	RenameAttributes *AttributeMapForSpans `yaml:"rename_attributes"`
+}
+
+// AttributeMapForSpans corresponds to a section representing a translation of
+// attributes for specific spans.
+type AttributeMapForSpans struct {
+	ApplyToSpans []types.SpanName `yaml:"apply_to_spans"`
+	AttributeMap AttributeMap     `yaml:"attribute_map"`
 }
 
 // SpanEventsChange corresponds to a section representing span events change.

schema/v1.0/parser_test.go

@@ -75,10 +75,11 @@ func TestParseSchemaFile(t *testing.T) {
 				Spans: ast.Spans{
 					Changes: []ast.SpansChange{
 						{
-							RenameAttributes: &ast.RenameAttributes{
+							RenameAttributes: &ast.AttributeMapForSpans{
 								AttributeMap: ast.AttributeMap{
 									"peer.service": "peer.service.name",
 								},
+								ApplyToSpans: []types.SpanName{"HTTP GET"},
 							},
 						},
 					},

schema/v1.0/testdata/valid-example.yaml

@@ -65,7 +65,9 @@ versions:
             # the new attribute name starting from this version.
             attribute_map:
               peer.service: peer.service.name
-
+            apply_to_spans:
+              # apply only to spans named "HTTP GET"
+              - "HTTP GET"
     span_events:
       changes:
         # Sequence of translations to apply to convert the schema from a prior version