Is your feature request related to a problem? Please describe.
Would be nice if plugins can add/change some of the webpacking configuration ability...

Describe the solution you'd like
I would suggest that certain of the fields in the webpack.config file be changeable by some json settings; either as part of the actual plugin package.json file itself; or a hook during install updates the fields in a global application wide webpack json file.

For example:
https://github.com/NativeScript/nativescript-dev-webpack/blob/master/templates/webpack.javascript.js#L213

For my sqlite plugin, I would like to add:
**.sqlite to the Glob pattern; in addition I would like to add some files to the externals, but the new configuration file appears to be controlled exclusively by environmental variables, which makes it even harder for users to follow my documentation as they need to add two externals for at least one of my plugins. If this could be controlled by plugins, then these externals (& glob patterns) could be "installed" with part of the plugin and the end user wouldn't have to do anything...

Describe alternatives you've considered
Rewriting the config file using a hook, to add the missing pieces; but this seems very error prone.