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/analysis/internal/flatten/schutils/flatten_schema.go

@@ -0,0 +1,29 @@
+// Package schutils provides tools to save or clone a schema
+// when flattening a spec.
+package schutils
+
+import (
+	"github.com/go-openapi/spec"
+	"github.com/go-openapi/swag"
+)
+
+// Save registers a schema as an entry in spec #/definitions
+func Save(sp *spec.Swagger, name string, schema *spec.Schema) {
+	if schema == nil {
+		return
+	}
+
+	if sp.Definitions == nil {
+		sp.Definitions = make(map[string]spec.Schema, 150)
+	}
+
+	sp.Definitions[name] = *schema
+}
+
+// Clone deep-clones a schema
+func Clone(schema *spec.Schema) *spec.Schema {
+	var sch spec.Schema
+	_ = swag.FromDynamicJSON(schema, &sch)
+
+	return &sch
+}