[NestJS] slack bot 연동하기

Incoming Webhooks

$ npm i @slack/client
$ npm i nestjs-slack-webhook

[nest, sentry, slack 연동 blog] https://velog.io/@1yongs_/NestJS-sentry-slack-error%EB%A1%9C%EA%B7%B8-%EC%88%98%EC%A7%91