feat: graceful exit terminal

[rishabh3112]

What kind of change does this PR introduce?
feature

Did you add tests for your changes?
WIP
If relevant, did you update the documentation?

Summary
Added code for graceful exit.
For reference: https://github.com/webpack/webpack-dev-server/blob/75999bb9bb8803de633fcb037405f45a5bf7d029/lib/Server.js#L1808-L1838

Does this PR introduce a breaking change?
Yup can be for tools that consume webpack-cli's output.

Other information
/cc @alexander-akait

[rishabh3112]

@alexander-akait should we add flag to enable this behavior as dev server does?
If we keep it by default, it can be a breaking change for tools that rely on webpack-cli's output.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.48%. Comparing base (d242dea) to head (9ea48e7).
Report is 908 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/webpack-cli/src/webpack-cli.ts	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3075      +/-   ##
==========================================
- Coverage   91.50%   91.48%   -0.03%     
==========================================
  Files          23       23              
  Lines        1719     1738      +19     
  Branches      519      524       +5     
==========================================
+ Hits         1573     1590      +17     
- Misses        146      148       +2     

Files with missing lines	Coverage Δ
packages/webpack-cli/src/webpack-cli.ts	93.96% <90.00%> (-0.09%)	⬇️

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[alexander-akait]

Looks good, let's add couple tests - just create custom plugin with infinity waiting and send SIGINT signals to close it

[rishabh3112]

/cc @alexander-akait

[evenstensberg]

could you rebase?

[evenstensberg]

No activity, closing.