feat: Sub-Store 生成的订阅地址支持传入 订阅链接/User-Agent/节点内容 可以复用此订阅的其他设置

例如: 建一个 name 为 sub 的订阅, 配置好节点操作

以后可以自由传入参数 无需在 Sub-Store 前端创建新的配置

`/download/sub?target=Surge&content=encodeURIComponent编码过的本地节点`

`/download/sub?target=Surge&url=encodeURIComponent编码过的订阅链接&ua=encodeURIComponent编码过的User-Agent`

backend/src/restful/sync.js

@@ -22,14 +22,18 @@ export default function register($app) {
     $app.get('/api/sync/artifact/:name', syncArtifact);
 }
 
-async function produceArtifact({ type, name, platform }) {
+async function produceArtifact({ type, name, platform, url, ua, content }) {
     platform = platform || 'JSON';
 
     if (type === 'subscription') {
         const allSubs = $.read(SUBS_KEY);
         const sub = findByName(allSubs, name);
         let raw;
-        if (sub.source === 'local') {
+        if (url) {
+            raw = await download(url, ua);
+        } else if (content) {
+            raw = content;
+        } else if (sub.source === 'local') {
             raw = sub.content;
         } else {
             raw = await download(sub.url, sub.ua);