fix: add test for generator field and remove internalSrcFolder usage

[khendrikse]

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Summary

• Remove the feat: Make additional function attributes available via functions manifest zip-it-and-ship-it#1221 isInternal and internalSrcFolder configuration options.
• Checks for generator option with integration test

Connected to:

• https://github.com/netlify/pod-compute/issues/350
• feat: add generator as an option to config and save it in the manifest and remove isInternal zip-it-and-ship-it#1341

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[github-actions]

This pull request adds or modifies JavaScript (.js, .cjs, .mjs) files.
Consider converting them to TypeScript.

[eduardoboucas]

Left a question about a test, but LGTM otherwise.

[eduardoboucas]

Why are you removing this test? I thought this was testing the deploy configuration API?

[khendrikse]

I made the same test a part of another test I wrote :) so now we have one test with both a snapshot and different field checks :)