Add initial support for OpenSubsonic. (#2302)

server/subsonic/opensubsonic.go

@@ -0,0 +1,13 @@
+package subsonic
+
+import (
+	"net/http"
+
+	"github.com/navidrome/navidrome/server/subsonic/responses"
+)
+
+func (api *Router) GetOpenSubsonicExtensions(_ *http.Request) (*responses.Subsonic, error) {
+	response := newResponse()
+	response.OpenSubsonicExtensions = &responses.OpenSubsonicExtensions{}
+	return response, nil
+}