feat(Rest): expose https.Agent options (#6177)

Co-authored-by: Antonio Román <kyradiscord@gmail.com>

typings/index.d.ts

@@ -47,6 +47,7 @@ import {
   Snowflake,
 } from 'discord-api-types/v9';
 import { EventEmitter } from 'events';
+import { AgentOptions } from 'https';
 import { Stream } from 'stream';
 import { MessagePort, Worker } from 'worker_threads';
 import * as WebSocket from 'ws';
@@ -3893,6 +3894,7 @@ export interface HTTPErrorData {
 }
 
 export interface HTTPOptions {
+  agent?: Omit<AgentOptions, 'keepAlive'>;
   api?: string;
   version?: number;
   host?: string;