chore: reorganize configuration and source files to allow for multiple sub-apps

[kgryte]

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read and understand the Code of Conduct.
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• Searched for existing issues and pull requests before submitting this pull request.
• Filed an issue (or an issue already existed) prior to submitting this pull request.
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Description

What is the purpose of this pull request?

This pull request:

• reorganizes Webpack configuration to allow for other future SPAs which may handle other aspects of the documentation (e.g., tutorials, recipes, how-to guides, contributor docs, etc). It does so by moving the content in /etc/webpack to a sub-folder api-docs.
• refactors the various Webpack config files which were auto-generated by "create React app" such that the various stuff we actually care about and need to update is at the top of the various config files, rather than buried within the various config files. While these files are somewhat an abomination, this is a small step to making them easier to maintain while they are still around.
• moves the API docs SPA source files from src/ to src/api-docs. Again, this is to allow for the possibility of creating separate SPAs for the various documentation needs we will have moving forward.

Related Issues

Does this pull request have any related issues?

This pull request:

• is tangentially related to Multiple Versions: Support for docs for multiple stdlib versions #101 in that it is part of a wider effort to improve stdlib documentation.

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

I checked that everything still built by running make api-docs-app. While I did not attempt to view the end product in a web browser, at minimum, the app successfully built without any errors in the terminal.

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@stdlib-js/reviewers

[kgryte]

cc @batpigandme for visibility