Update hot reload docs for Webpack 5 and Yarn 2

[brandonchinn178]

Supercedes #1568

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[x] Docs
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #1554, nestjs/nest#5928, nestjs/nest-cli#1000

What is the new behavior?

Docs are now up to date for Yarn 2 and Webpack 5.

Until nestjs/nest-cli#1000 is merged, you'll need to do webpack@5.9.0 instead of webpack. See that PR for repro steps following these docs

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[Lowfly]

Please valid this PR, it has been really useful for me !