feat: allow providing single or multi prompts (#1866)

* Add new type to handle single or multi prompts

* update docs

* apply review

taskfile/ast/prompt.go

@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"gopkg.in/yaml.v3"
+
+	"github.com/go-task/task/v3/errors"
+)
+
+type Prompt []string
+
+func (p *Prompt) UnmarshalYAML(node *yaml.Node) error {
+	switch node.Kind {
+	case yaml.ScalarNode:
+		var str string
+		if err := node.Decode(&str); err != nil {
+			return errors.NewTaskfileDecodeError(err, node)
+		}
+		*p = []string{str}
+		return nil
+	case yaml.SequenceNode:
+		var list []string
+		if err := node.Decode(&list); err != nil {
+			return errors.NewTaskfileDecodeError(err, node)
+		}
+		*p = list
+		return nil
+	}
+	return errors.NewTaskfileDecodeError(nil, node).WithTypeMessage("prompt")
+}