feat: add envinfo as webpack-cli info command

[tabrindle]

What kind of change does this PR introduce?
This adds a new feature: a webpack-cli info command which outputs something like this:

  System:
    OS: macOS High Sierra 10.13
    CPU: x64 Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz
  Binaries:
    Node: 8.10.0
    Yarn: 1.5.1
    npm: 5.6.0
  Browsers:
    Chrome: 65.0.3325.181
    Firefox: 58.0
    Safari: 11.0
  npmPackages:
    webpack:
      wanted: ^4.1.1
      installed: 4.1.1
    webpack-addons:
      wanted: ^1.1.5
      installed: 1.1.5
    webpack-dev-server:
      wanted: ^3.0.0
      installed: 3.1.1
  npmGlobalPackages:
    webpack: 4.2.0
    webpack-cli: 2.0.11

Did you add tests for your changes?
Not sure necessary - if any objections, I am open to looking into this.

If relevant, did you update the documentation?
Updated ISSUE_TEMPLATE

Summary
Should help with issue reporting: see #334

Does this PR introduce a breaking change?
Nope.

Other information
This same approach has been successful in Jest, styled-components, create-react-app and React Native so far, I'd like to bring it to webpack!

[jsf-clabot]

All committers have signed the CLA.

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[evenstensberg]

Thanks for submitting a PR @tabrindle ! ❤️

[webpack-bot]

Hi @tabrindle.

Just a little hint from a friendly bot about the best practice when submitting pull requests:

Don't submit pull request from your own master branch. It's recommended to create a feature branch for the PR.

You don't have to change it for this PR, just make sure to follow this hint the next time you submit a PR.

[evenstensberg]

🎉 This PR is included in version 2.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀