image level lint: enforce manifest mandatory annotations

closes #536

Signed-off-by: Lisca Ana-Roberta <ana.kagome@yahoo.com>

pkg/test/mocks/lint_mock.go

@@ -0,0 +1,18 @@
+package mocks
+
+import (
+	godigest "github.com/opencontainers/go-digest"
+	"zotregistry.io/zot/pkg/storage"
+)
+
+type MockedLint struct {
+	LintFn func(repo string, manifestDigest godigest.Digest, imageStore storage.ImageStore) (bool, error)
+}
+
+func (lint MockedLint) Lint(repo string, manifestDigest godigest.Digest, imageStore storage.ImageStore) (bool, error) {
+	if lint.LintFn != nil {
+		return lint.LintFn(repo, manifestDigest, imageStore)
+	}
+
+	return false, nil
+}