feat(plugin-webpack): add devContentSecurityPolicy config option

[malept]

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• The changes are appropriately documented (if applicable).

Summarize your changes:

Fixes #2331 (probably). At the very least, it allows for a workaround.

This is difficult to test automatically, because it's an option passed to webpack-dev-server.

This needs to be documented in the Webpack plugin guide.

[codecov]

Codecov Report

Merging #2332 (4e5e427) into master (6e0a624) will increase coverage by 2.37%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2332      +/-   ##
==========================================
+ Coverage   73.19%   75.56%   +2.37%     
==========================================
  Files          74       74              
  Lines        2197     2202       +5     
  Branches      414      415       +1     
==========================================
+ Hits         1608     1664      +56     
- Misses        418      421       +3     
+ Partials      171      117      -54     

Impacted Files	Coverage Δ
packages/plugin/webpack/src/WebpackPlugin.ts	58.46% <0.00%> (-0.33%)	⬇️
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	97.05% <0.00%> (+5.88%)	⬆️
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	87.34% <0.00%> (+20.25%)	⬆️
packages/api/core/src/api/publish.ts	92.10% <0.00%> (+22.36%)	⬆️

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