feat: add --from flag, refactor source providers (#2610)

Signed-off-by: Keith Zantow <kzantow@gmail.com>

cmd/syft/internal/options/source.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 
 	"github.com/scylladb/go-set/strset"
+
+	"github.com/anchore/syft/syft/source/sourceproviders"
 )
 
 type sourceConfig struct {
@@ -25,12 +27,13 @@ type imageSource struct {
 }
 
 func defaultSourceConfig() sourceConfig {
+	var digests []string
+	for _, alg := range sourceproviders.DefaultConfig().DigestAlgorithms {
+		digests = append(digests, alg.String())
+	}
 	return sourceConfig{
 		File: fileSource{
-			Digests: []string{"sha256"},
-		},
-		Image: imageSource{
-			DefaultPullSource: "",
+			Digests: digests,
 		},
 	}
 }