feat(metrics): add scheduler related metrics (#2076)

Signed-off-by: Alexei Dodon <adodon@cisco.com>

pkg/extensions/imagetrust/image_trust.go

@@ -5,6 +5,7 @@ package imagetrust
 
 import (
 	"context"
+	"fmt"
 	"time"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
@@ -274,3 +275,13 @@ func (validityT *validityTask) DoWork(ctx context.Context) error {
 
 	return nil
 }
+
+func (validityT *validityTask) String() string {
+	return fmt.Sprintf("{sigValidityTaskGenerator: %s, repo: %s}",
+		"signatures validity task", // description of generator's task purpose
+		validityT.repo.Name)
+}
+
+func (validityT *validityTask) Name() string {
+	return "SignatureValidityTask"
+}