feat: add modpack versions API endpoint

cmd/server/main.go

@@ -135,6 +135,7 @@ func main() {
 
 			r.Route("/modpacks", func(r chi.Router) {
 				r.Post("/import", modpackHandler.ImportModpack)
+				r.Get("/versions", modpackHandler.GetModpackVersions)
 			})
 
 			r.Route("/users", func(r chi.Router) {