feat(webdav): 添加Caddy WebDAV服务配置

新增webdav.yml部署文件及对应配置，包括：
- 添加WEBDAV_IMAGE_TAG环境变量
- 创建webdav.yml服务定义文件
- 添加webdav.conf配置文件实现基础认证和路由规则

webout/configs/caddy/webdav.conf

@@ -0,0 +1,20 @@
+# The Caddyfile is an easy way to configure your Caddy web server.
+{
+    order webdav before file_server
+}
+
+https://dav.48474.SITE:28443 {
+    tls  48474@qq.com
+    root * /webdav
+    encode zstd gzip
+    basicauth {
+        cnphpbb $2a$14$hRWtDnqpndGM5W4oMC8Do.H9FS/xydS3Djq8zswNgeVYSDgE1ldqm
+    }
+    route {
+        rewrite /dav /dav/
+        webdav /dav/* {
+            prefix /dav
+        }
+        file_server browse
+    }
+}