feat(plugin-webpack): allow most webpack-dev-server options to be configurable

[malept]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Fixes #594.
Fixes #2308.
Fixes #2413.

[codecov]

Codecov Report

Merging #2444 (d26bb26) into master (7063724) will increase coverage by 2.55%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #2444      +/-   ##
==========================================
+ Coverage   72.73%   75.29%   +2.55%     
==========================================
  Files          91       91              
  Lines        2344     2352       +8     
  Branches      440      441       +1     
==========================================
+ Hits         1705     1771      +66     
+ Misses        473      472       -1     
+ Partials      166      109      -57     

Impacted Files	Coverage Δ
packages/plugin/webpack/src/WebpackPlugin.ts	36.84% <66.66%> (+3.50%)	⬆️
packages/maker/base/src/Maker.ts	75.67% <0.00%> (-2.11%)	⬇️
packages/installer/darwin/src/InstallerDarwin.ts	31.57% <0.00%> (-1.76%)	⬇️
packages/api/core/src/util/upgrade-forge-config.ts	94.73% <0.00%> (-1.70%)	⬇️
packages/api/core/src/api/init.ts	97.56% <0.00%> (+4.87%)	⬆️
packages/api/core/src/api/make.ts	88.29% <0.00%> (+6.57%)	⬆️
packages/api/core/src/util/rebuild.ts	100.00% <0.00%> (+7.14%)	⬆️
packages/api/core/src/api/install.ts	94.87% <0.00%> (+16.66%)	⬆️
packages/api/core/src/api/start.ts	87.65% <0.00%> (+22.22%)	⬆️
... and 1 more

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[malept]

Documented at https://www.electronforge.io/config/plugins/webpack#dev-server