Add support for Fulcio and Rekor, and --sign-by-sigstore=param-file

(skopeo copy) and (skopeo sync) now support --sign-by-sigstore=param-file,
using the containers-sigstore-signing-params.yaml(5) file format.

That notably adds support for Fulcio and Rekor signing.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/go-openapi/runtime/logger/logger.go

@@ -0,0 +1,20 @@
+package logger
+
+import "os"
+
+type Logger interface {
+	Printf(format string, args ...interface{})
+	Debugf(format string, args ...interface{})
+}
+
+func DebugEnabled() bool {
+	d := os.Getenv("SWAGGER_DEBUG")
+	if d != "" && d != "false" && d != "0" {
+		return true
+	}
+	d = os.Getenv("DEBUG")
+	if d != "" && d != "false" && d != "0" {
+		return true
+	}
+	return false
+}