@angular-builders/custom-webpack upgrade webpack-merge

[andygup]

Is your feature request related to a problem? Please describe.
This is a request to upgrade custom-webpack to the latest version of webpack-merge. I did notice this dependabot PR => #814 but couldn't find any related issues.

Describe the solution you'd like
Use regular merge.

Describe alternatives you've considered
With Angular 10, we can run: ng build && webpack --config ./extra-webpack.config.js but that's bypassing the Builder approach and not ideal.

Additional context
We are having merge issues that I suspect might be related to the use of webpack-merge and smartStrategy, reference: https://github.com/just-jeb/angular-builders/blob/master/packages/custom-webpack/src/webpack-config-merger.ts#L2. This is based on 1 year old implementation that's been dropped from the latest version: survivejs/webpack-merge@1c1c2f1

[just-jeb]

Dropping smartStrategy is a breaking change, so I don't think it can be added as a minor version. It potentially can break a lot of builds, so it should be part of 11 release.

[just-jeb]

Closed with #907, you can try it in 11.0.0-beta.2. Refer to the migration guide for the docs.