feat(webpack): Expose webpack base config class

[juliendargelos]

Expose webpack base config class.

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

Add an export of the WebpackBaseConfig class.

It could be useful for some advanced modules to be able to extend this class for independent webpack build using Nuxt base config:
I'm making a module which hooks Nuxt to add another webpack build with NetlifyCMS, but sharing some source files with Nuxt project (for previews). I would like to have the same base configuration so Nuxt project files can be imported with the same rules, plugins, etc...

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: #)
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[codecov-io]

Codecov Report

Merging #5425 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #5425   +/-   ##
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  Coverage   96.16%   96.16%           
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  Files          74       74           
  Lines        2555     2555           
  Branches      652      652           
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  Hits         2457     2457           
  Misses         82       82           
  Partials       16       16

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[manniL]

Thanks for the PR!
We had a similar one at #5366 which has evolved to #5378 so far ☺️

I'd suggest to bring in your ideas and concerns there or create a more in-depth PR if the suggested changes are too different.

[pi0]

Thanks, @juliendargelos for this PR. I'm closing this to move to discuss in #5378.