Update webpack-dev-server documentation

[Alexander Akait]

Feature to document

All docs where we have dev server configurations

Author(s)

Any

Additional information

Migration guide - https://github.com/webpack/webpack-dev-server/blob/master/migration-v5.md

[ ] I am willing to work on this issue and submit a pull request.

/cc @snitin315 Will be great to help me here, thank you

[Nitin Kumar]

Yes, I will update the docs for dev server