Issue Templates: add option to have dropdown printed list (#31577)

Issue template dropdown can have many entries, and it could be better to
have them rendered as list later on if multi-select is enabled.

so this adds an option to the issue template engine to do so.

DOCS: https://gitea.com/gitea/docs/pulls/19

---

## demo:

```yaml
name: Name
title: Title
about: About
labels: ["label1", "label2"]
ref: Ref
body:
  - type: dropdown
    id: id6
    attributes:
      label: Label of dropdown (list)
      description: Description of dropdown
      multiple: true
      list: true
      options:
        - Option 1 of dropdown
        - Option 2 of dropdown
        - Option 3 of dropdown
        - Option 4 of dropdown
        - Option 5 of dropdown
        - Option 6 of dropdown
        - Option 7 of dropdown
        - Option 8 of dropdown
        - Option 9 of dropdown
```

![image](https://github.com/user-attachments/assets/102ed0f4-89da-420b-ab2a-1788b59676f9)

![image](https://github.com/user-attachments/assets/a2bdb14e-43ff-4cc6-9bbe-20244830453c)

---
*Sponsored by Kithara Software GmbH*

(cherry picked from commit 1064e817c4a6fa6eb5170143150505503c4ef6ed)

modules/issue/template/template.go

@@ -88,6 +88,9 @@ func validateYaml(template *api.IssueTemplate) error {
 			if err := validateBoolItem(position, field.Attributes, "multiple"); err != nil {
 				return err
 			}
+			if err := validateBoolItem(position, field.Attributes, "list"); err != nil {
+				return err
+			}
 			if err := validateOptions(field, idx); err != nil {
 				return err
 			}
@@ -340,7 +343,13 @@ func (f *valuedField) WriteTo(builder *strings.Builder) {
 			}
 		}
 		if len(checkeds) > 0 {
+			if list, ok := f.Attributes["list"].(bool); ok && list {
+				for _, check := range checkeds {
+					_, _ = fmt.Fprintf(builder, "- %s\n", check)
+				}
+			} else {
 				_, _ = fmt.Fprintf(builder, "%s\n", strings.Join(checkeds, ", "))
+			}
 		} else {
 			_, _ = fmt.Fprint(builder, blankPlaceholder)
 		}

modules/issue/template/template_test.go

@@ -216,6 +216,20 @@ body:
 `,
 			wantErr: "body[0](dropdown): 'multiple' should be a bool",
 		},
+		{
+			name: "dropdown invalid list",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "dropdown"
+    id: "1"
+    attributes:
+      label: "a"
+      list: "on"
+`,
+			wantErr: "body[0](dropdown): 'list' should be a bool",
+		},
 		{
 			name: "checkboxes invalid description",
 			content: `
@@ -807,7 +821,7 @@ body:
   - type: dropdown
     id: id5
     attributes:
-      label: Label of dropdown
+      label: Label of dropdown (one line)
       description: Description of dropdown
       multiple: true
       options:
@@ -816,8 +830,21 @@ body:
         - Option 3 of dropdown
     validations:
       required: true
-  - type: checkboxes
+  - type: dropdown
     id: id6
+    attributes:
+      label: Label of dropdown (list)
+      description: Description of dropdown
+      multiple: true
+      list: true
+      options:
+        - Option 1 of dropdown
+        - Option 2 of dropdown
+        - Option 3 of dropdown
+    validations:
+      required: true
+  - type: checkboxes
+    id: id7
     attributes:
       label: Label of checkboxes
       description: Description of checkboxes
@@ -836,8 +863,9 @@ body:
 					"form-field-id3":   {"Value of id3"},
 					"form-field-id4":   {"Value of id4"},
 					"form-field-id5":   {"0,1"},
-					"form-field-id6-0": {"on"},
+					"form-field-id6":   {"1,2"},
-					"form-field-id6-2": {"on"},
+					"form-field-id7-0": {"on"},
+					"form-field-id7-2": {"on"},
 				},
 			},
 
@@ -849,10 +877,15 @@ body:
 
 Value of id4
 
-### Label of dropdown
+### Label of dropdown (one line)
 
 Option 1 of dropdown, Option 2 of dropdown
 
+### Label of dropdown (list)
+
+- Option 2 of dropdown
+- Option 3 of dropdown
+
 ### Label of checkboxes
 
 - [x] Option 1 of checkboxes