feat(subsonic): support form post (#1333)

* feat(subsonic): support form post

---------

Co-authored-by: jeffvli <jeffvictorli@gmail.com>

src/renderer/api/subsonic/subsonic-controller.ts

@@ -997,6 +997,10 @@ export const SubsonicController: InternalControllerEndpoint = {
             features.lyricsMultipleStructured = [1];
         }
 
+        if (subsonicFeatures[SubsonicExtensions.FORM_POST]) {
+            features.formPost = [1];
+        }
+
         return { features, id: apiClientProps.server?.id, version: ping.body.serverVersion };
     },
     getSimilarSongs: async (args) => {