Move webpack-cli as a dependency

[vhiairrassary]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

Is there any test I can add to be confident with that change?

Motivation / Use-Case

#2256

webpack-cli is required at https://github.com/webpack/webpack-dev-server/blob/master/bin/webpack-dev-server.js#L65 but it is listed as a devDependencies and not as a dependencies which is not compatible with Yarn PnP.

Feel free to close this PR if it does not make sense.

Breaking Changes

I have not enough knowledge about webpack-dev-server's internal to answer this.

[jsf-clabot]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

[codecov]

Codecov Report

Merging #2257 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2257   +/-   ##
======================================
  Coverage    93.9%   93.9%           
======================================
  Files          34      34           
  Lines        1280    1280           
  Branches      368     368           
======================================
  Hits         1202    1202           
  Misses         71      71           
  Partials        7       7

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9d1c6d2...f9bcb84. Read the comment docs.