Preview images for Issue cards in Project Board view (#22112)

Original Issue: https://github.com/go-gitea/gitea/issues/22102

This addition would be a big benefit for design and art teams using the
issue tracking.

The preview will be the latest "image type" attachments on an issue-
simple, and allows for automatic updates of the cover image as issue
progress is made!

This would make Gitea competitive with Trello... wouldn't it be amazing
to say goodbye to Atlassian products? Ha.

First image is the most recent, the SQL will fetch up to 5 latest images
(URL string).

All images supported by browsers plus upcoming formats: *.avif *.bmp
*.gif *.jpg *.jpeg *.jxl *.png *.svg *.webp

The CSS will try to center-align images until it cannot, then it will
left align with overflow hidden. Single images get to be slightly
larger!

Tested so far on: Chrome, Firefox, Android Chrome, Android Firefox.

Current revision with light and dark themes:

![image](https://user-images.githubusercontent.com/24665/207066878-58e6bf73-0c93-4caa-8d40-38f4432b3578.png)


![image](https://user-images.githubusercontent.com/24665/207066555-293f65c3-e706-4888-8516-de8ec632d638.png)

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

models/migrations/v1_19/v241.go

@@ -0,0 +1,17 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_19 //nolint
+
+import (
+	"xorm.io/xorm"
+)
+
+// AddCardTypeToProjectTable: add CardType column, setting existing rows to CardTypeTextOnly
+func AddCardTypeToProjectTable(x *xorm.Engine) error {
+	type Project struct {
+		CardType int `xorm:"NOT NULL"`
+	}
+
+	return x.Sync(new(Project))
+}