feat: Put request rate limit at application server (#3857)

* feat: Put request rate limit at application server

This PR contains implementation for a blanket rate limiter at
application server level. Currently the allowed throughput is set high
only to be changed later as per the actual data gathered.

* Simplify implementation

1. Remove shutdown handler to purge rate limiter keys
2. Have separate keys for default and custom(route-based) rate limiters
3. Do not kill default rate limiter because it is not needed anymore due
   to (2) above

* Set 60s as default for rate limiting window

* Fix env types

server/routes/api/index.ts

@@ -5,6 +5,7 @@ import env from "@server/env";
 import { NotFoundError } from "@server/errors";
 import errorHandling from "@server/middlewares/errorHandling";
 import methodOverride from "@server/middlewares/methodOverride";
+import { rateLimiter } from "@server/middlewares/rateLimiter";
 import apiKeys from "./apiKeys";
 import attachments from "./attachments";
 import auth from "./auth";
@@ -80,6 +81,8 @@ router.post("*", (ctx) => {
   ctx.throw(NotFoundError("Endpoint not found"));
 });
 
+api.use(rateLimiter());
+
 // Router is embedded in a Koa application wrapper, because koa-router does not
 // allow middleware to catch any routes which were not explicitly defined.
 api.use(router.routes());