fix: allow overriding all "webpackConfig" options

[rchl]

Apart from allowing all webpackConfig options to be overridden, also
deprecate "webpackConfig" and other publish-release-specific options
and accept a configuration object for the "publishRelease" option.

[codecov]

Codecov Report

Merging #338 (eaf2544) into master (d344d6f) will increase coverage by 4.68%.
The diff coverage is 87.50%.

❗ Current head eaf2544 differs from pull request most recent head 08d0b61. Consider uploading reports for the commit 08d0b61 to get more accurate results

@@            Coverage Diff             @@
##           master     #338      +/-   ##
==========================================
+ Coverage   69.23%   73.91%   +4.68%     
==========================================
  Files           1        1              
  Lines          39       46       +7     
  Branches       19       21       +2     
==========================================
+ Hits           27       34       +7     
  Misses          9        9              
  Partials        3        3              

Impacted Files	Coverage Δ
lib/module.js	73.91% <87.50%> (+4.68%)	⬆️

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