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
```
---
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