Support Issue forms and PR forms (#20987)

* feat: extend issue template for yaml

* feat: support yaml template

* feat: render form to markdown

* feat: support yaml template for pr

* chore: rename to Fields

* feat: template unmarshal

* feat: split template

* feat: render to markdown

* feat: use full name as template file name

* chore: remove useless file

* feat: use dropdown of fomantic ui

* feat: update input style

* docs: more comments

* fix: render text without render

* chore: fix lint error

* fix: support use description as about in markdown

* fix: add field class in form

* chore: generate swagger

* feat: validate template

* feat: support is_nummber and regex

* test: fix broken unit tests

* fix: ignore empty body of md template

* fix: make multiple easymde editors work in one page

* feat: better UI

* fix: js error in pr form

* chore: generate swagger

* feat: support regex validation

* chore: generate swagger

* fix: refresh each markdown editor

* chore: give up required validation

* fix: correct issue template candidates

* fix: correct checkboxes style

* chore: ignore .hugo_build.lock in docs

* docs: separate out a new doc for merge templates

* docs: introduce syntax of yaml template

* feat: show a alert for invalid templates

* test: add case for a valid template

* fix: correct attributes of required checkbox

* fix: add class not-under-easymde for dropzone

* fix: use more back-quotes

* chore: remove translation in zh-CN

* fix EasyMDE statusbar margin

* fix: remove repeated blocks

* fix: reuse regex for quotes

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/issue/fields/checkboxes.tmpl

@@ -0,0 +1,12 @@
+<div class="field">
+	{{template "repo/issue/fields/header" .}}
+	{{$field := .}}
+	{{range $i, $opt := .Attributes.options}}
+		<div class="field">
+			<div class="ui checkbox">
+				<input type="checkbox" name="form-field-{{$field.ID}}-{{$i}}" {{if $opt.required}}readonly checked{{end}}>
+				<label>{{$opt.label}}</label>
+			</div>
+		</div>
+	{{end}}
+</div>

templates/repo/issue/fields/dropdown.tmpl

@@ -0,0 +1,14 @@
+<div class="field">
+	{{template "repo/issue/fields/header" .}}
+	{{/* FIXME: required validation */}}
+	<div class="ui fluid selection dropdown {{if .Attributes.multiple}}multiple clearable{{end}}">
+		<input type="hidden" name="form-field-{{.ID}}" value="0">
+		<i class="dropdown icon"></i>
+		<div class="default text"></div>
+		<div class="menu">
+			{{range $i, $opt := .Attributes.options}}
+				<div class="item" data-value="{{$i}}">{{$opt}}</div>
+			{{end}}
+		</div>
+	</div>
+</div>

templates/repo/issue/fields/header.tmpl

@@ -0,0 +1,6 @@
+{{if .Attributes.label}}
+	<h3>{{.Attributes.label}}{{if .Validations.required}}<label class="required"></label>{{end}}</h3>
+{{end}}
+{{if .Attributes.description}}
+	<span class="help">{{RenderMarkdownToHtml .Attributes.description}}</span>
+{{end}}

templates/repo/issue/fields/input.tmpl

@@ -0,0 +1,4 @@
+<div class="field">
+	{{template "repo/issue/fields/header" .}}
+	<input type="{{if .Validations.is_number}}number{{else}}text{{end}}" name="form-field-{{.ID}}" placeholder="{{.Attributes.placeholder}}" value="{{.Attributes.value}}" {{if .Validations.required}}required{{end}} {{if .Validations.regex}}pattern="{{.Validations.regex}}" title="{{.Validations.regex}}"{{end}}>
+</div>

templates/repo/issue/fields/markdown.tmpl

@@ -0,0 +1,3 @@
+<div class="field">
+	<div>{{RenderMarkdownToHtml .Attributes.value}}</div>
+</div>

templates/repo/issue/fields/textarea.tmpl

@@ -0,0 +1,6 @@
+<div class="field">
+	{{template "repo/issue/fields/header" .}}
+	{{/* FIXME: preview markdown result */}}
+	{{/* FIXME: required validation for markdown editor */}}
+	<textarea name="form-field-{{.ID}}" placeholder="{{.Attributes.placeholder}}" class="edit_area {{if .Attributes.render}}no-easymde{{end}}" {{if and .Validations.required .Attributes.render}}required{{end}}>{{.Attributes.value}}</textarea>
+</div>