feat: add WEBPACK_PACKAGE env var to use custom webpack package

[snitin315]

What kind of change does this PR introduce?
feature

Did you add tests for your changes?
Yes

If relevant, did you update the documentation?
will send PR to documentation
Summary
FIxes #2551

"webpack": "^4.0.0",
"webpack5": "npm:webpack@^5.28.0",
"webpack-cli": "^4.5.0"

webpack - run webpack 4
WEBPACK_PACKAGE=webpack5 - run webpack 5

Does this PR introduce a breaking change?
No

Other information
No

[alexander-akait]

Need test, test/build/custom-webpack/custom-webpack.js with module.exports = require('webpack') and set WEBPACK_PACKAGE=./custom-webpack.js

[codecov]

Codecov Report

Merging #2556 (38cddca) into master (d039472) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2556      +/-   ##
==========================================
+ Coverage   90.98%   91.12%   +0.13%     
==========================================
  Files          29       29              
  Lines        1464     1464              
  Branches      419      420       +1     
==========================================
+ Hits         1332     1334       +2     
+ Misses        132      130       -2     

Impacted Files	Coverage Δ
packages/webpack-cli/lib/webpack-cli.js	92.41% <100.00%> (ø)
packages/webpack-cli/lib/bootstrap.js	100.00% <0.00%> (+20.00%)	⬆️

---

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 d039472...38cddca. Read the comment docs.

[snitin315]

added tests 👍🏻

[snitin315]

Cache issue?

[alexander-akait]

Yep, happens only on windows

[alexander-akait]

@snitin315 Let's wait green #2553 and merge, then rebase

[anshumanv]

lets rebase