chore: allow unmarshaling the Discussion form template

This is was largely generated through GPT-4.1, with some tweaks to
handle the `validations` key.

Although my preference would be to use [0] and [1] (via [2]), it
unfortunately doesn't handle the complex `if`s.

This is a separate commit to isolate LLM-generated code.

[0]: https://www.jvt.me/posts/2025/06/05/json-schema-go/
[1]: https://json.schemastore.org/github-issue-forms.json
[2]: github/docs#37424

Co-authored-by: gpt-4.1 <github-copilot@jamietanna.co.uk>

Author: jamietanna

internal/discussionform/main.go

@@ -0,0 +1,91 @@
+package discussionform
+
+import (
+	"fmt"
+	"gopkg.in/yaml.v3"
+)
+
+type BodyItem struct {
+	Type        string
+	Item        any
+	Validations map[string]bool
+}
+
+func (b *BodyItem) UnmarshalYAML(value *yaml.Node) error {
+	var typeHolder struct {
+		Type string `yaml:"type"`
+	}
+	if err := value.Decode(&typeHolder); err != nil {
+		return err
+	}
+	b.Type = typeHolder.Type
+
+	var validationsHolder struct {
+		Validations map[string]bool `yaml:"validations"`
+	}
+	if err := value.Decode(&validationsHolder); err != nil {
+		return err
+	}
+	b.Validations = validationsHolder.Validations
+
+	switch typeHolder.Type {
+	case "dropdown":
+		var dropdown Dropdown
+		if err := value.Decode(&dropdown); err != nil {
+			return err
+		}
+		b.Item = dropdown
+	case "input":
+		var input Input
+		if err := value.Decode(&input); err != nil {
+			return err
+		}
+		b.Item = input
+	case "textarea":
+		var textarea Textarea
+		if err := value.Decode(&textarea); err != nil {
+			return err
+		}
+		b.Item = textarea
+	default:
+		return fmt.Errorf("unknown type: %s", typeHolder.Type)
+	}
+	return nil
+}
+
+type Dropdown struct {
+	Type       string             `yaml:"type"`
+	ID         string             `yaml:"id"`
+	Attributes DropdownAttributes `yaml:"attributes"`
+}
+
+type DropdownAttributes struct {
+	Label   string   `yaml:"label"`
+	Options []string `yaml:"options"`
+}
+
+type Input struct {
+	Type       string          `yaml:"type"`
+	ID         string          `yaml:"id"`
+	Attributes InputAttributes `yaml:"attributes"`
+}
+
+type InputAttributes struct {
+	Label string `yaml:"label"`
+}
+
+type Textarea struct {
+	Type       string             `yaml:"type"`
+	ID         string             `yaml:"id"`
+	Attributes TextareaAttributes `yaml:"attributes"`
+}
+
+type TextareaAttributes struct {
+	Label       string `yaml:"label"`
+	Description string `yaml:"description"`
+	Value       string `yaml:"value"`
+}
+
+type Template struct {
+	Body []BodyItem `yaml:"body"`
+}