Implement /api/v1/instance/peers (#2913)

* Implement /api/v1/instance/peers

* Use punycode

* Remove Cache-Control

* Rename

src/server/api/index.ts

@@ -46,6 +46,8 @@ router.post('/signin', require('./private/signin').default);
 router.use(require('./service/github').routes());
 router.use(require('./service/twitter').routes());
 
+router.use(require('./mastodon').routes());
+
 // Return 404 for unknown API
 router.all('*', async ctx => {
 	ctx.status = 404;