feat: allow specific description for CLI options

[snitin315]

What kind of change does this PR introduce?
Feature

• add cliDescription - Sometimes we need specific descriptions for CLI options, for example when we are deprecating a CLI option only in favor of another

  • fix: mark --open-app deprecated in favor of --open-app-name webpack-dev-server#4091
  • fix: update --web-socket-server description webpack-dev-server#4098

• add negatedDescription - webpack-cli creates a negative flag for each boolean flag, it uses negatedDescription property for description if available.

Did you add tests for your changes?
Yes

Does this PR introduce a breaking change?
No

What needs to be documented once your changes are merged?

It is for internal usage, nothing to be documented.

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[snitin315]

@sokra, thanks for the update.

[sokra]

Thanks