refactor: convert postman case

hrp/pkg/convert/to_yaml.go

@@ -0,0 +1,13 @@
+package convert
+
+import "github.com/httprunner/httprunner/v4/hrp/internal/builtin"
+
+// convert TCase to YAML case
+func (c *TCaseConverter) toYAML() (string, error) {
+	yamlPath := c.genOutputPath(suffixYAML)
+	err := builtin.Dump2YAML(c.tCase, yamlPath)
+	if err != nil {
+		return "", err
+	}
+	return yamlPath, nil
+}