fix(deps)!: make @sentry/webpack-plugin a peer dependency

[rchl]

BREAKING CHANGE: To use the "publishRelease" option, it's now necessary to manually install the @sentry/webpack-plugin package as a dev dependency.

This is in response to Sentry change getsentry/sentry-webpack-plugin#343 which inadvertently made webpack dependencies get installed in production.

[codecov]

Codecov Report

Merging #390 (b6fe2c9) into master (f72147f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #390   +/-   ##
=======================================
  Coverage   71.42%   71.42%           
=======================================
  Files           1        1           
  Lines          49       49           
  Branches       23       23           
=======================================
  Hits           35       35           
  Misses         11       11           
  Partials        3        3           

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[rchl]

While Sentry reverted their change, it is still technically more correct to list @sentry/webpack-plugin as a peer dependency as it's not required for normal operation of the module and should only really be required on building. This will also remove further dependencies from production.