refactor(python): use once + debug for License acquired from METADATA... logs (#8175)

pkg/dependency/parser/python/packaging/parse.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"net/textproto"
 	"strings"
+	"sync"
 
 	"golang.org/x/xerrors"
 
@@ -15,6 +16,8 @@ import (
 	xio "github.com/aquasecurity/trivy/pkg/x/io"
 )
 
+var licenseMetadataInfoOnce sync.Once
+
 type Parser struct {
 	logger *log.Logger
 }
@@ -70,7 +73,10 @@ func (p *Parser) Parse(r xio.ReadSeekerAt) ([]ftypes.Package, []ftypes.Dependenc
 
 		if l := h.Get("License"); l != "" {
 			if len(licenses) != 0 {
-				p.logger.Info("License acquired from METADATA classifiers may be subject to additional terms",
+				licenseMetadataInfoOnce.Do(func() {
+					p.logger.Info("Licenses acquired from one or more METADATA files may be subject to additional terms. Use `--debug` flag to see all affected packages.")
+				})
+				p.logger.Debug("License acquired from METADATA classifiers may be subject to additional terms",
 					log.String("name", name), log.String("version", version))
 			} else {
 				license = l